The ability to procreate for many species existing across the Multiverse far surpassed that of humans.
Even if human possessed a hormonal system that allowed them to be sexually receptive throughout the year, each gestation period required at least nine to ten months and usually resulted in the birth of a single infant on each occasion. Basically, humans' ability for reproduction was very weak, especially when compared to other species that could breed without breaks. It would already be considered frequent for them to do so two or three times consecutively, with the possibility of some individuals having no adaptability when it came to breeding.
