Mooshroom Cows no longer spawn on mycelium at light level 9 or higher in 1.16.1

I spent a while flying around a mushroom biome and didn't find any mooshrooms, day or night. Is it possible that this is just a consequence of passive mob spawning in general being relatively rare?

Passive mob spawning after initial generation is very slow, and has been since Beta 1.8 - this is intentional, you are supposed to breed them.