Hmmm, well for the original question, I'd counter it by saying "why do people like The Sims?" that's pretty much what The Survival genere is in a nutshell when you get down to it. For the most part your spending a lot of time with a toolbox trying to complete your own perfect little project and living space. Inevitably once your done you want to try and build something else, and well... there you go. This whole game style seems like someone pretty much decided to make "The Sims" more of a game where you control one character, and there are more hardcore penalties for failing to meet the needs of the character your controlling, as well as making things more challenging by inserting elements that are going to try and mess up your stuff and force you to be more careful. The increased gamability drew more people into what was already a fairly successful genere to begin with. The increasing multiplayer options are simply born of the same desire a lot of people have had to share their Sims creations already, and presumably to also be able to mess with someone. Making it ultimately easier than ever before for community projects, or so you can show off your highly customized Nazi SS War Crimes camp that you lovingly constructed based on holocaust footage... or that giant golden lava-spewing wang Yahtzee mentioned as a possibility in his Minecraft review for that matter.... along with other more sane creations of course. I suppose "Second Life with the ability to shoot people in the face" also fits to an extent but it's not quite big enough and with almost all of these games in early access it remains to be seen if the creation tools will ever get that good, or will simply remain at the whole "blocks and crafting" level.
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As far as the Zombie Apocalypse goes I have to say I've had similar thoughts for a very long time myself, and have not been shy about sharing them. To me the issue with the portrayal isn't so much the "wiping out huge amounts of people" aspect of things, but rather the state of affairs persisting as long as it does. Assuming any people are left, especially some of those with resources, things are going to be brought under some degree of control, and honestly you'd probably have more to worry about from whomever has the biggest group of organized gun wielders and is putting together the new emergency government than anything. Typically such things fall apart from me when you see things like "The Walking Dead" where we're supposed to believe zombies overran hardened military positions or somehow overcame tanks, without any real justification for how that occurs. What's more the whole "trope" of them being relentless and endless and having to run from them as an unconfrontable force of nature makes no real sense, because their numbers are in fact quite limited. A comparatively small group of armed people could very well clear out entire areas of them, rather than needing to run away, and indeed it would be considerably more efficient. I find it eye rolling when you see things like the remake of "Dawn of The Dead" (I think it was) when some dude presumably fires off several thousand rounds of ammo from his roof... an accomplished sharpshooter pretty much dropping one per shot, and doesn't make any dent in the horde... that's just beyond belief because really you drop several thousand people (that's more than many might think) and it's going to have a definite impact on the population of most areas, especially the town around your average suburban shopping mall.
That said the initial outbreak and a short term apocalyptic crisis is easy to justify, giving people a few months of hell and depopulating the world. In a lot of zombie fiction the central set up is that the virus has a very short incubation time before causing a lethal response and reanimation, unlike rabies, also unlike rabies there is no real cure at the time it happens. It follows a sort of "hot zone" type route where by the time it's known it already has been carried to the far corners of the earth and is spreading exponentially through the population.... or basically a bunch of people get infected, keel over, die, and then get up and start killing the comparatively small population of people that are at least immune to the airborn form (but presumably not to the direct injection into the bloodstream via saliva or other bodily fluids). It's been known for a long time that a virus could in theory wiped out huge amounts of humanity VERY quickly, and indeed it's the basis for biological warfare and why there is a global ban on it. Indeed a lot of zombie virus stories approach it from the avenue that it's a biological weapons experiment that gets out of hand. Or the unexpected results of medical research, after all being able to repair necrotized tissue is one of the holy grails of medical science and actually would do a LOT for humanity, with some imagination you could see how such an experiment MIGHT lead to a zombie outbreak if all of the safeguards somehow failed or terrorists weaponized it or whatever (though real world safeguards are far more intense than in movies, making a lot of these scenarios kind of implausible since it would take a lot more than one greedy researcher or whatever).
Another popular bit with zombie outbreaks is to justify it as a sort of "slow burn" which is to say that the initial form of the virus has a long incubation time before it kills and re-animates, though storywise it rapidly mutates later to spread quicker for it's own survival. The idea being that when the epidemic starts people just know there is some kind of flu-like epidemic on the loose, and have no idea it's lethal on the level you eventually see or causes re-animation. This means you start seeing the sick people brought into hospitals (in highly urban areas) and when they fill up shipped out to emergency camps, and even military bases which are oftentimes designated for crisis situations like this. As a result when people start dying, and re-animating, and the virus mutates to spread quicker and pass from bite to bite, the zombies are already in the middle of most of the most effective people to deal with it, who are also blindsided, and as a result most of the soldiers, police, firemen, doctors, etc... who were tapped for the crisis die first and/or have the highest concentrations of zombies in them, actually moving outward from the places of safety (which also means a lot of people that aren't effective wind up fleeing into the hordes trying to get to refuges that were the first to fall).
The point is it's easy to justify the deaths of billions of people with just a nasty virus without even needing the zombies. The problem of course being with the zombies when you add them as the primary problem after the spread, is that even if .1% of the population survived there shouldn't be much of an issue within a couple of months, well other than the impact of large scale depopulation, forming new governments, and similar things. Nobody would likely be forced to flee encroaching hordes, or live like a scavenging nomad unless they wanted to (which some people might, as it does have a sort of appeal for those with an independent spirit).