Why did Super Sketch Bob take 10 years to make?
"Life, uh, gets in the way" -Jeff Goldblum, probably
Super Sketch Bob started out as a the manic fever dream of a twenty-something wannabe game designer with way too much time on her hands and finished development as the manic fever dream of a thirty-something wannabe game designer with absolutely no time on her hands.
What a long strange road it's been.
If you beat the game at any %, you can actually visit the Super Sketch Museum in the last world which has a room with a timeline dedicated to answering this very question.