In addition to that, some (many?) entrepreneurs build something users want and see their apps grow. But, then, they see their friends doing something else that's growing even faster. And, being optimists, decide that they can run two projects at the same time. So they launch a pet project so as not to miss out on that other opportunity. I've done it, and I know a lot of excellent entrepreneurs do it.
The thing is, it's sometimes the right thing to do. My last pet project grew much faster than my main project, and it ended up being my main project. And I'm happy it happened that way. But there is no way to know in advance how it's going to go.
