I'm gonna go devils advocate here.
I think at first glance this is exactly how you might perceive a move like this, and I don't mean to be patronize, not just at first glance, but at 2nd, 3rd, 4th and 5th glance you'd be thinking exactly what you wrote, and it's a sound analysis for sure. What I would say, is that I don't know if this indicates what people might believe it does. We like to imagine that the top of these publishers are bumbling idiots without enough brains between them to screw in a light bulb (without bringing up micro-transactions at least). And I'm not even saying that this is the case with this article, what I'm trying to say is let's say that quotes and history aside, one of the largest game companies in the world made the largest purchase in gaming history. They did it to buy something unpopular with it's fan base and seem to be moving in a direction that enthusiasts don't particularly like. So there isn't much to like about this, in fact there is plenty of reason to speculate that this will result in a lot of things that many of the enthusiast community will hate to see happen.
So why do this? We are left with two possibilities; first is that those at Activision don't understand all of the above, and they saw something shiny and are hoping they can make it more shiny, and the second is that they are hoping for something that outweighs the costs, both physical and PR wise. I'm inclined to think that the latter is probably true.
First of all, PR when it comes to game companies translates to very little when discussing how business decisions relate to actual revenue. Lets be realistic. Sometimes the best business decisions are not the most popular ones. Steve Jobs, who must have an actual religious following by now among the business community was responsible from some deeply unpopular decisions surrounding the devices that made him famous. All of these are all but lost in the wake of Apple's success but if you were following them through out you can probably remember. It is not to say that PR doesn't influence decisions, of course it does, but the true industry shifts are not generally impacted. The unpopularity of the "free to play" business model as compared to the inversely proportional revenue it produces is as close as you will get to proof of this concept within our industry. But this just shoot's down a "why not."
To get to the "why?" of it all, you have to look beyond what king produces because everyone is focusing on candy crush as a product in itself. The popularity of candy crush is not spectacular because of its popularity. It's spectacular because of who it's audience is composed of. That audience is not an audience that read's this sight, nor is it the audience that picked up Halo last week. It's the audience that reads Kim Kardashian Gossip, and picks up their kids from soccer practice. I don't mean that in a patronizing way. They have disposable income, smartphones, and specific hours of the day they wish to kill. It is specifically targeting people who are not susceptible to the "mind games" of games. That's one demographic Activision barely touches. They have the core market because if Diablo 3 proved anything, it's that Blizzard could proposition their fan's to lick they're boot's clean of dog shit, and their fans will thank god it's only a dog's shit.
That's one angle that hasn't been touched on is that 6 billion is an indicator that they are making a very long term investment. That investment isn't that Candy Crush will be around forever, but it does mean that they think that the smartphone market will likely not change much over the next 6 or so years. That even the devices a decade from now will go largely unchanged from their current state. Touch screen's will not likely fade out of existence of the next decade, and it is much more likely that we will see devices that are easier for the demographic that king aims for to use and play and capitalize on. Is that worth 6 billion dollars? Absolutely. Activision can pump out about a billion dollars a year in profits if they're on their game, in fact for a company that pulls their kind of numbers without king, they could see as much as 2 billion dollars in profits, and while that would be impressive, it wouldn't be ridiculous or unheard of. Keep in mind that this is without a couple of years of Candy Crush money which will likely produce a sizable chunk in addition to that even if it's audience was cut in half.
A gamble? sure. A dumb Gamble? I'm not so sure it is.
That's my two cents though.
