I'd guess that there are a lot of factors involved here, with space one of them for some people. I doubt it's a significant factor though - it's too much of a coincidence in my mind to think that an entire hobby's worth of people, that have been running along happily for 15-20 years without a problem, just so happens to have run out of space at the exact same time that post-covid and a cost of living crisis has hit. People used to just sell then replace to get around the space problem, but selling is now an issue in that equation.
As I went through that list adding up the prices though, a lot of them are modern - it was very noticeable versus how the list would have looked 5 or 10 years ago, that the amount of money people had tied up in machines was therefore far greater than it used to be. In the past. I guess historically the average person might have had £5-10k in total tied up in machines, whereas in that list they can have that tied up in a single game.
My guess is that this is all mainly just a hangover from covid when people had masses of disposable income and so dropping that sort of money on a game seemed fine (people who did that, don't feel bad about it - my wife spunked £10k on a hot tub that we can barely justify turning on because electricity is so expensive!!), but now there's a fraction of that disposable income left in the market.
It's noticeably getting worse too. There were 3 pages of machines available for sale only a month or so ago when I last looked, and 4 pages now. There's always historically been a summer lull in sales, but I'd guess that an increase of a net 15-20 open adverts in a month, to a list that started at around 60 machines for sale, is a massive record for pinballinfo.