Especially in terms of online games there are different kinds of money-making-systems behind them to make the actual game financially worth being programmed.
Some games have annoying advertising that does not limit your performance but your ability to enjoy the game and sometimes also is not properly placed so loading problems and errors may occur.
Other games charge you to get items or levels that you need to actually be able to be good at the game. This is especially frustrating because, if you quit half way, after you found out you can't afford the game or don't have any pleasure in buying your win, you have that ugly feeling of lacking closure.
Online games are constantly developing and provide (best case) service, updates and challenges. And those who use this service a lot should pay more for it than those who don't.
Give people a trial time to see whether they want to play the game. Develop modern micro-payment systems and this can be fair and easy alternative to other business concepts for online games.
What games charge you for the hour? I know plenty of the online only games have set subscription periods 1 week and month etc... In which your still paying for a considerable amount of time you won't use, due to real life during that time period.
Any company stupid enough to try a pay by the hour scheme, would not be able to handle the public backlash of such a scheme.
Although I did find this article about rental games on the PSN:
The problem with cash shops and whatnot is you force the player to constantly have to break immersion to think about real life money.
You don't want your gamer to constantly be worried about how much money they are wasting, you don't want them to break their immersion.
With a monthly sub fee you pay it and forget about it for a whole month, and with single player you buy the game and never think about that money again (unless it's a bad game you think that was a waste of money).
Also, what about AFKing, Socializing, waiting for respawns, ect.
That would drive people away from your game instantly.