I don’t see that at all. My kids were in sororities and they are 25 years old. IMO, both were not that involved in their houses while in college and have a few friends but not a lot. They both stayed in because they see how close I am with the friends I went to school with 40+ years ago. Same with my niece and nephew who also enjoyed it in college but not aren’t that involved. (except my nephew is in a lot of weddings)
With my own group of alums, we have younger women joining and even leading events. They are young professionals who are still looking to be in a social and philanthropic group. They want to raise money or volunteer for events. During covid, one took it on to raise money for meals for floors of nurses (a couple were also members). As you said, she asked and out came the checkbooks.
When Harvard tried to punish fraternity and sororities for not going co-ed, Harvard lost (in state and federal court). The students wanted the formal, organized badges and gavels. They want to be able to form their own groups of friends for whatever purpose without interference. They want to join national organization and not just rely on forming their own groups of friends, co-ed or not.
Darthmouth tried requiring the co-ed thing and it didn’t work there either.