I think that the main problem is that there are now far more passengers wishing to use the non airline lounges-pay to use is a relatively new concept for most of them. This is especially at “leisure” airports where people see the use of a business lounge as a great start to their holiday. And the number and capacity of lounges generally hasn’t increased despite this.
I get PP via my black Amex card and haven’t had a problem with it so far- although I tend only to need it in far flung destinations. I’d be disappointed if Amex dropped it.