Sheer force of will mostly. It can also be a lot of fun but mostly the fun part is publishing something nobody has seen or done before

Make a little progress every day and eventually you will have a full replay. I've also realized that I find it much more satisfying to make one big replay than spending an equal ammount of time and energy making 10 small ones.

It can be a very interesting experience aswell. Even I still learn stuff about the game with every advanced replay I make, it's like unravelling an enigma. Pieces fall into place and sometimes you can use those new pieces to create cool shit which feels very good