Gotham Central wrote:
1) Why weren't more of the aliens depicted in the RecDeck scene used in other places in the film? The Rec Deck scene gives the impression of a fairly diverse crew for the Enterprise, yet once she is underway, just about all of the aliens disappear
In addition to the other explanations offered, it was stated that many of the people wearing those costumes were not really actors, but well-known fans (ie. Bjo Trimble) or authors such as David Gerrold. These people were given a small part in the movie as a "thank you" for their years of support.
As to why nobody else ever wore those costumes... maybe they were constructed to fit a particular person?
In-universe, I'm not entirely sure how Deltan society manages to function, though. One description I read of them -- from the novelization perhaps -- says that to Deltans, sex was part of literally every interaction between people and as common as a handshake. Ok, how many people do you casually interact with in a day? How many people do you shake hands with? Imagine if literally every single one of those encounters involved you having sex with them. How would anything ever get done?
Not all sexual acts or encounters involve going to bed/having actual intercourse.