Explain the feature in as much detail as possible

It is strange that there are almost no sheep on the grassland. I used BOP, Traverse, Climate Biome2, Sakura, and Floricraft. These modules have added more than 100 new biomes.
There are only SAVANNA, MESA, and HILL fields in the configuration file. Is it only suitable for vanilla? Or is it judged based on some attributes of the formation, such as humidity, temperature, etc.?
By the way, there is no Mushroom Cow on Mushroom Island, which is really weird to me.