"What if the cockroach had really large wings? No, that would make it even more disgusting! What if the very large wings had some pretty colors? Oh, then we would love it! Or... not. What do you think? A butterfly-looking insect that nested inside the walls and flew around indoors and left teeny tiny turds on the counter... we'd hate that too, right? Why do indoorsy insects look so drab? So we don't kill them. What an impossible evolutionary road it would be to tart up sufficiently that we'd refrain from smushing them. Drab is the way to go, for the lowly cockroach. And come to think of it, refrain from flying. That will only activate your antagonists."
A meditation, posted by me, at Facebook, a propos of a news story, "It's So Hot Out Cockroaches Might Start Flying in NYC/All American cockroaches have wings and the ability to take flight, but don't typically do so unless they're in humid climates."