I go to between 6 and 8 festivals a year. Normally one "biggish" one (eg Bearded, Wickham, Boomtown) and lots of small DIY punk etc festivals. Going Feral last month raised £1,000 for a mental health charity, despite being maybe 150 under capacity (guessing). At least one is a private party, rather than a festival, which gives you an indication of the sort of size involved!
I'm surprised at a figure of 100 festivals that have shut, but I'm probably not in the loop on a lot of festivals further north or "the wrong genre". What I can say is that one festival I had pencilled in for this year got cancelled. Another had to find a new site at very short notice due to excessive council demands, and numbers have been falling steadily at the one festival I go to every year. I see a lot of FB posts plugging tickets just days before the festival [eta - Wickham started today and they have posted today on FB offering tix] . Nothing sells out, I don't think, other than Glastonbury, (maybe a few others - I think BD and BT ran out of campervan tickets, but not admission).
Reasons? There's a lot of festivals out there, maybe there were just too many for them all to survive. Costs are certainly up, but the cost of living crisis means many people have to ration themselves and can't afford higher ticket prices. It's not just the ticket cost, it's getting there and then buying food/drink/merch. Too many commercial festivals take the piss with food and drink prices, which puts people off.
I'm confident that the independent DIY festival scene is immune from big business interference and will survive, possibly in a slimmed down way though, if there's no money around.