I’ve also witnessed app developers grow envious of others that have rewarded ads in their apps and I must say, I really want to try it sometime too.
I tend to stick to apps that have a purpose and bring real meaning and so games are not my thing at the moment.
Using the Admob console for example it’s possible to restrict the amount of ads/rewards that is offered to the user over a time period.
This limit is used on occasions where you would not want the user to acquire too much wealth in a game over a rather short time frame.
Otherwise the user could complete the game quicker than anticipated and move along on to something else.
Developers need to keep the user engaged for as long as possible and continue earning an income so this restriction is usually always wise to implement.