[nobody9999]

>I always wondered if there could be some sort of in-world explanation as to why all the aliens in star trek/wars are so ...humanoid.

I'd say that for most Sci-Fi Movies/TV there's a couple of reasons:

1. Non-humanoids are less relatable than humanoids;

2. Budgetary restrictions and the relative immaturity of CGI holds us back from creating fairly realistic and relatable alien species.

[interestica]

Yes, that's the real reasons. But by 'in-world' I meant something that could be explained within the story/world-building to justify/explain it away.

[nobody9999]

I know. I just thought I'd throw that out there since no one else did.