I've been a co creator on a game that's been in the works for about 10 years now, we finally started making real progress 3 years ago. It requires so much research, planning, and many many drafts let alone future fine tuning. I had to get better at drawing, developing designs, research many things about what and why characters look like.
It's something that I do because I want to bring to life this project, and it's an active part of my life.
It takes a lot of steps, so it naturally became time consuming. I am still passionate today as I was 10 years ago when the project was just a pipe dream. It was a place to escape to, something personal to grow. It was fun as it was difficult to create something, so I would say it naturally became something that takes many years to truly come to life.