Some hostile mobs spawns rarely some doesn't spawn

I play always on normal difficulty and zombies, skeletons, creepers and spiders spawns rare but enderman didn't spawn. I don't know how about husks and strays because I have not been to desert and snow biomes yet in version 1.5 phase 2. Bty endermans also didn't spawn in nether. I use Samsung Galaxy J7 2017. Ps only Drowneds spawns like crazy in normal difficulty.