These are all good examples. And I agree that budgetary considerations also play a part.
But I would have to add that the belief that drama is about character, meaning the regular cast characters. This school of thought contains both producers and viewers. As near as I can tell, most of the hostility to stand-alone episodes comes from disinterest in any characters other than the ones the viewer has invested in (basically, "strangers.")
And yet another factor I think is a sociopolitical rejection of the role of people en masse. These producers may not be so blatantly ideological as to use terms like rabble or mob. But there is a powerful tendency to view people in general wholly negatively, prone to riot or panic or deluded by demagogues or all simultaneously. Salvation for the plot is to come only from the Hero, the true Leader. The unvirtuous leaders' are pretty much all-powerful (like Section 31,) while the virtuous leaders oppose the abuses of power. But never, never are the people an independent factor, much less the saviors. This tendency is barely present in Star Trek but it is fairly prominent in later Treks and stuff like the new BattleStar Galactica.
PS No one knows what the future is right, which means right there that most SF can't be genuinely realistic. It's pseudorealistic. What's the value in that? The only thing that easily comes to mind is that speculation about the future can provoke thought about where we are going. But if all the fictional science is just dismissed as "technobabble," it's not going to be relevant to that. There really is for most TV and movie SF a genuine question as to what point there is to the SF trappings other than badly conceived coolness. Everyone who really takes "technobabble" to encapsulate some sort of criterion of good writing is actually arguing for bad writing. Being so horribly confused in public should be kind of embarrassing.
