Pigeons are notoriously bad at building nests, because they don’t have to good like other birds.they are descendants of Rock Doves (kewl name for a band) and like their ancestors the just need a flat surface and are use to dealing with meager building materials. They use what they have for a “good enough for me” nest and pigeons being almost everywhere in the world means their nests do just fine.

Nope. If you look it up there's serveral instances of rock pigeons making "nests" like this, it's legitimately just a thing they do specifically.

These birds are known for being terrible nest makers. But maybe you're on to something, maybe they don't realize they're pregnant until it's too late.