I have experience there since I work as a game designer currently for an MMO PC game for children.
The thing is...game designers don't want popups in your face constantly asking you to pay money with a bunch of in-game currency. They usually want to make a good game first and foremost. The issue is, most of the time the company they work for or the company investing in or publishing the game requires game designers to add that in because when you get to the bottom line, the companies have to make money and support their workers.
It is especially tricky with the game I work for because we make games for kids and you have to be careful.
Just from my own experience, most game designers working for a company are forced to put monetization tactics in or else the game will not get made.
That said though, mobile literally is the dumping ground of horribly made games by companies and people looking to get rich quick and be the next fad.
Luckily I am working for an MMO and it's more stable than mobile. I don't even bother much with mobile anymore. It's just too difficult to muddle through all the trash to find one decent thing.
There are a lot of free puzzle games though if you're just looking for an on the bus time killer. It's hard to screw up a basic puzzle game.