A lot of endangered species are specialists instead of generalists. Why do you think that is the case?

Maybe because these particular cells die faster than other cells in the body, for example the receptors cells in your nasal cavity only lasts for about 3-4 weeks and after that it dies, therefore new news are formed every week in order to keep your nasal cavity from deteriorating your smell ability.
Some blood cells only lasts for about 120 days that's why new cells are formed and produced, faster production means faster cell division.

It depends on the type of cell and the current situation of those cells.