I think that's one of the bad parts about the way Star Trek portrays alien races.
If they are just alien race of the week, they'll be a planet of hats variety alien.
http://tvtropes.org/pmwiki/pmwiki.php/Main/PlanetOfHats
The only times a alien gets fleshed out is if they are a major recurring race like the Bajorans, Founders, Jem'Hadar.
Another bad part about dealing with exploring with lots of random aliens is that the writers like to follow that trope and run with it.
It's harder to create a society and fill it with logical details. It's easier to make a alien race that fills out whatever message you want to send.
I do love Babylon 5 for how it protrayed it's races with far more detail. I know they did sometimes fall into the Planet of Hats trope, but it still added alot more detail than most and it did shift the hats around to some degree.
The problem is that "Planet of Hats" trope is that it comes down to stereo typing a Culture / Ethnicity / some specific group. It's too easy and common to do this. Many writers are very guilty of this. Heck most of us are probably guilty of it to some degree in our daily lives.
I do love what ENT did with the 'Suliban'. They showed the cabal and the regular folk. It was a nice portrayal of multiple facets of the same alien.