I chose 320 x 180 because of Animal Well. In fact, the whole app was originally conceived as a way for me to make an Animal Well style game, but more conveniently than using Pico8 (Billy Basso implied once that he used Pico8 to prototype Animal Well before moving to C++). I still think 320 x 180 is the right size for both games and game makers.
For example, here's a very early (mostly broken) prototype of 90s.dev
Because of 320x180, it can fit the code editor and the mapmaker or spritemaker on the screen at once, and each tab is big enough to be usable.