It's another, less significant version of pay-to-win. It might be a free game at first glance, but after playing for a few levels it becomes pay-to-win because things would get increasingly harder which forces you to pay.
Most of these are mobile games, as PC game makers would rather charge you, but iirc some takes form of DLCs.

Capitalism, eh?
Ethan: Dude I cannot break this level it is so goddamn hard!
Me: These MMORPGs are pay-to-progress man, if you don't pay, you just can never break this level. Things that are free are the most expensive, you know.
Get the Pay-to-progress mug.