Mainly, inspiring constraints. Because PICO-8 is not very capable, it feels like a success to accomplish very simple tasks, but also:
- it's not too hard to accomplish those simple tasks (we made a countdown timer!), and
- if you really want, you can really push it (we made a polynomial interpolation function for smoothly animating motions of objects!).

(We haven't tried pygame, though - we don't actually know Python, so.)