A couple of years ago, when I was playing Pokemon Go daily, I showed up to a raid with my son. I started chatting with some of the other people there and one guy mentioned that his monthly budget for the game was $100. Another guy chimed in to concur. It was kind of eye opening. I had been wondering how the game could be free, and it was at that moment that I realized that the game was mostly paid for by hard core players who were spending to level up faster and get rarer Pokemon (through buying incubators for eggs and such).
Pokemon Go doesn't really have a gambling aspect to it though, so I can't fault it in that area, nor am I really sure their model is a problem - since the people spending the money are choosing to do so for their own entertainment. It does feel a bit odd though, and ultimately it did hurt the experience of the game (since you do better if you pay more).