On top of that, there’s the very real possibility of people gaining fame faster than they can spend it.
Depending on a lot of factors such as how much you play, how hard you farm chest events, what classes you like the most (that is to say, which items you could never consider feeding because you like the class that uses them too much)… it’s not hard to be in a position where you just don’t get good fp items often enough to spend your fame and prevent it from accumulating.
That’s mostly my own experience with making a f2p pet and I don’t know how many other people are the same, though.