Development studios and developers in general release a product, spend countless hours working on said product, and release a free game. They become millionaires right? Not quite. You see in this scenario they’ve made nothing in return from a game or product you’re using.
In the case of most “free” games you can play through and win them if you’re extremely dedicated, or like most of the people who win the games you can finally pay a little to purchase an upgrade inside the application.
This is a very cool model in which you get to try before you buy, however people spend an inordinate amount of space berating developers who might stand to make $5-10 in in-app purchases from a game that you will literally sit and play glued to your device for weeks.
Everyone on the internet seems to feel entitled to everything NOW, FREE, screw you developer, and when their developer goes away they wonder why that person could have been so cruel as to make the thing require payment after a point.
Now, I’ll give you that on children’s games this is an insidious practice. I don’t think there should ever be an app aimed at kids that requires in-apps to progress past a certain point, but these reviewers are, for the most part, adults who would probably like to get paid for their time and effort in producing something.
Imagine a store gave you unlimited free hotdogs but charged for a drink. In this case the drink is you getting better. You can bring your own drink, which makes traveling a little more difficult, or you can purchase a drink from the nice people who are giving you your fix and potentially keep them in business to start an ice cream shop.
Now, there are some complaints that are valid – such as hiding more and more purchases behind a wall in which you only realize there’re more to buy after you’ve plunked down some money, but for the most part complaining about an app trying to make enough money to pay the developer makes the reviewer look stupid.