The point is that games require you to spend 100 hours for "ridiculous grind" for no other reason than to motivate you to pay to not grind. If paying was not an option, the game would be designed to not require any non-enjoyable grinding/waiting (even if there is grinding, it would be an enjoyable part of the gameplay, not just "wait 5 minutes and you can click something again").
Imagine a game where you build a village. You need gold to build something. The game gives you X gold every 5 minutes, and you can pay to get more. Sounds reasonable, right? Except that there is no gameplay reason for you to wait 5 minutes to get more gold. They could just as well give you more every 30 seconds and the gameplay would became 10 times faster and more enjoyable.
If there is no option to pay with money, there would not be any need to pay with time either.