...you're reading
waay to much into RNG, very basic spawn rules and magic borders of Galactic Sectors that even the legacy Biologicals firmly adhered to
What we haven't seen yet is actual, procedural Biological life with a realistic propagation and distribution in the Galaxy without fixed borders.
PS.
We also haven't encountered any standard technological race, not even an Earth-like World with lights on its dark side.
Seems the Plants ate them all.