I'm happy to pay for a game I enjoy playing, the game is made F2P, it becomes inundated with Eternal September players, it is no longer fun to play, I am annoyed.

The changes made when games go F2P tend to change the product you paid for in significant ways, often in ways that some players will think ruin it.

There's a reason I haven't played TF2 in years, and it's not because I'm indignant that others didn't have to pay for it.

As a long time player I'll say that surfing definitely increased by a lot when it went free to play, it's not entirely sunk cost fallacy. Im high enough now that it's not much of an issue but lower ranks are rife with surfing and even in my diamond 1 games I see them enough to be annoying, at least.