These strategies aren’t particularly complicated or technical, they are just well refined pieces of psychological persuasion. In particular, the “reward removal” ploy quoted above comes straight from the minds of the arcade game cabinet makers. It’s “insert coin to continue” in a different presentation. You invest so much time into a game that you’d rather pay a little to keep going, than forfeit your progress.
Imagine a freemium word processor where you have to pay to save your file.