I agree there are not that many teaching nuns any longer, but I do know they are still teaching at my alma mater High School and probably about the same proportion as when I was there in the 70s. That school is run by the School Sisters of Notre Dame, and has been for nearly 100 years, teaching does matter to them.
Oh, I didn’t mean that teaching didn’t matter to them, they are just too few in number. And aging fast. My sons attended a Jesuit HS, and even there the faculty is mostly “lay teachers”. And now the Principal is a layperson too.