Why can a decrease in the number of a species cause its extinction?

A decrease in the number of any species can lead to the extinction of this species. After all, if, for example, there are very few lions, and many of them, for example, sick or of the same sex, then how will they reproduce? That is, their number will only decrease, which will lead to the fact that their species will not remain at all.

Nowadays, more and more animal species are dying out, because people kill them, for themselves, for leather bags, for fashionistas’ fur coats, if we hadn’t exterminated them like that, then many species would still be.