I think some of the older performers are there trying to kid themselves about how youthful they are. To me they are just embarrassing.
Perhaps it's because I went camping when I was at school that I never felt the desire to go to any festivals, and perhaps because I'm not a smoker, nor drug user, nor heavy drinker, and the whole 'muddy field' etc holds zero interest.
I suppose if I was staying in a B+B nearby, I might just consider one, but even 30 years ago I didn't have any inclination, and neither did work colleagues or before that, those I studied with.
It gets so much hype from the media because for them it is probably relatively cheap entertainment to fill hours of output without having to do much more than arrange a few presenters don't get legless before they are on radio/TV (and there may be a few who are suffering the effects that manage to wing it, even getting to do the same thing the following year).
As for the possibility of being jealous, no, I can think of dozens of better ways to use the money it would cost to go to Glastonbury and would really need to be paid to attend as I'd consider it a bit of a chore.