For the 1st issue:
in real life this is mostly for budget and practical reasons. Non-human aliens are MUCH more expensive to do properly. It is also much harder to get a good performance out of them.
in sci fi terms though, although they are still too human, there actually is pretty good reason to believe that humanoid form would dominate. To summarize: intelligent life obviously needs a big brain, and optimally this will be situated near all the major senses (so sight, smell, taste, sound). They'll also want stereoscopic vision and sound, but not to spend lots of energy on redundancy, so 2 eyes and 2 ears. You'll also want your vision situated high up, so as the head. So already we have a head, in the same general place as ours, featuring 2 ears, 2 eyes, their digestion intake (aka mouth), and likely the respiratory intake for smell (aka nose). As to the rest of the body, you need locomotion and ability to manipulate objects, but you again don't want to waste time on extra limbs. Bipedal locomotion works perfectly fine, so 2 legs is likely which will likely be stronger due to needing to carry the body mass all the time. Up to this point everything is in twos, so symmetry makes it highly likely you'd have 2 manipulating limbs as well and this is just more useful in general anyway. Then you get into other things. Also, sound is a very useful form of communication so it is likely they will speak in some form. So, you end up with a pretty humanoid creature. Now of course all of this is just conjecture from what we know, but we do lead pretty close to human like.
And keep in mind, particularly star wars, shows a fair chunk of variation (probably due to better budget for the most part or being animated), but even star trek often showed non humanoid intelligent aliens too, they just weren't common. And of course in star trek they even threw in the explanation that an ancient alien raced seeded the galaxy with their genes so that drove similar evolution, but that was mostly a retcon explanation.
For the 2nd issue:
The depends a lot on the series whether this is a good critique or not. For Star Trek for instance, they are dealing nearly universally with deep space faring societies due to the prime directive and 1st contact rules so yeah, they've gotten globally united most the time, and even in Star Trek they showed often this wasn't perfect and there was split planets between factions. Same holds pretty true for Star Wars where there has been galactic civilization for millennia. Babylon 5 from what I recall rarely dealt with anyone but the main races who were all stellar empires at that point. Firefly I suppose you could argue this pretty well though as the idea of nations was more inter-planetary rather than with a planet but I didn't watch much firefly to be sure.
Edit: I should note though if the issue is more just size, yeah, space faring Sci Fi always seems to seriously under use the size of planets. Seems everything always happens within the same areas and such. And going down to a planet it always seems they are just where the weird thing is going to happen. Now, often they do explain this adequately, but rarely do they actually deal with the size of the planet. Instead they work around it.