They kept changing the rules
I was a great fan of Farmville at one point, loving the game and playing it. I paid for a little bit of a boost now and then, but most things were achievable through a bit of work. However, they kept changing the rules. More and more of the nice items started being achievable by pay only, and then some of the basic achievements were only possible by parting with cash. It was like playing darts when the dartboard was on the back of a lama which was walking away from you.
Net result ... I switched off to their games and stopped playing them completely. End of revenue stream from me.