Because when you make stuff for yourself, you won’t have to wait to find an audience for yourself.
You can iterate and improve it fast because there will be a real user from day one.
It is also smart because when you make stuff for yourself, you also make it for those others like you.
Then it’s only a matter of them finding you or you finding them.
Which is not too difficult and simple enough to learn.
So in a way by making stuff for yourself, you set yourself up for success.