OK, OK, OK.
Now, what can WE do about all this?
When did you last chat to a nervous looking new club member, or a student, or someone else who looked a bit lonely at a flying club? When did you last offer to take someone flying with you, someone you don't know or who you just met, I mean? When did you last give advice to a newish PPL who wasn't sure whether they should fly, who was being ignored by instructors as they weren't a student any more?
"They" can't do everything. Maybe "we" can help. Way back, another PPL and I persuaded a school to put up a notice for people to sign if they wanted to share flights. I don't know if it worked or not, but we told the school they'd get more flying hourts booked that way, and they liked the idea.
I spend quite a lot of time chatting to people at flying schools. But I think I'm quite unusual - an extravert who likes chatting to people as much as I like flying. Some of them seem quite relieved to be talked to, especially if they're very young, very old, or female. There's a reason why "girlz" don't feel at home in flying schools. We get ignored, far too much of the time.
All the other reasons we've mentioned apply, but the lack of a social scene definitely doesn't help, and...dare I say it...flying folk are not always the most friendly, until they know you've done enough flying to be an anorak.