There are more casinos than we might think with such terms. The aim of the higher fees seems to be to get the account off their books by charging high fees with the intent that the account will zero out, and they can then close it. I expect most inactive accounts have an amount too small to be withdrawn, and will be wiped clean within a couple of months at these high fees.
Intercasino used to charge $2 per month after a number of months of inactivity.
The easy way to prevent this, and keep the balance intact, is to log in to each account at least once every couple of months, and make a single minimum wager. This renders the account "active".
I am sure this hurts US players the most, as they find it hard to deposit and withdraw, and may prefer to leave balances around in case they feel the urge to play again.
The publicity surrounding this issue is going to encourage players to do the sensible thing, and withdraw if they are not intending to play again within the next week (assuming all WR are met). This will end up costing the casino more in the long term, even if it starts to encourage more common sense among players when it comes to leaving balances hanging around for months.
Some casinos have even worse terms than this, they will confiscate the entire balance of an inactive account in one go.