Here's my explanation (don't take this too seriously) A lot of black people are Muslims and Muslims don't drink. Maybe that's why you don't meet them in bars.
I really doubt that the developers are racists, they probably didn't even think about what proportion of the Sirius Sector inhabitants should be what race. I haven't noticed any openly gay NPCs, does that mean the developers hate homosexuals?
Trent hardly comes in contact with a representative slice of the sector's population. Out of 220,000,000 people on Manhattan he meets maybe a dozen.
Let's get those missiles ready to destroy the universe!!