This is true. I guess when it comes to something that would take as long as a game, though, I feel like I'd want the entire thing to be something new and original instead of a spinoff or derivative of someone else's work. But you're probably right. I spend enough time fangirling over other series that making something based off them probably makes way more sense to get started.
It was an effort, getting a Feebas, then a Milotic!!! (Way way WAY to many hours spent doing that). But I did feel rather happy with myself when I completed it.
It's not like you need to make it based off what someone else made its more of the process to get you inspiring and excited to get something going.
Plus if youre fangirling you may as well go uber fangirl and make a fangirl game! The process will definitely get you inspired and may get you thinking of your own ideas!