This is true in 20w20b, as well. It looks like drowned only consider river and frozen_river as valid spawn biomes. If you place a drowned mob spawner underwater in either of those biomes, it spawn drowneds as expected. Place one in, say, ocean or deep_ocean, and...nothing. There may be other spawning mechanics that bypass the biome check, since I do occasionally see a drowned in the world, but I expect this is what's making them so rare and preventing drowned spawners from working.
QuarterAnimal
This is true in 20w20b, as well. It looks like drowned only consider river and frozen_river as valid spawn biomes. If you place a drowned mob spawner underwater in either of those biomes, it spawn drowneds as expected. Place one in, say, ocean or deep_ocean, and...nothing. There may be other spawning mechanics that bypass the biome check, since I do occasionally see a drowned in the world, but I expect this is what's making them so rare and preventing drowned spawners from working.Nope. I'm wrong.