Mobs barely spawns on a lot of biomes (except grass land)

This is something which i'm not sure if it's a bug but for the most part, it's what has made exploration worse for me on MCBE compared to Java. Mobs very rarely spawns (i gave a picture of the savanna biome. In my opinion, it has the worst spawn rate of any biome)  and when they do, they spawn in a group less than what i saw those playing on Java