I'm working on a small game right now (probably 3 or 4 hours in length) and the amount of work to do to get it to an acceptable state for release is gigantic. And that's after some serious downsizing in content.
Another game I'm playing and enjoying right now is Hollow Knight, which started off as a poorly received game jam entry , then a Kickstarter which raised a modest sum (less than 50K), and now it's a highly acclaimed title with nearly 3 million units sold (https://en.wikipedia.org/wiki/Hollow_Knight).
Celeste probably didn't have a Kickstarter because the studio behind it (Matt Makes Games) was already pretty mature, having already shipped hits like Towerfall. Contrast that to Hollow Knight's Team Cherry who basically had to bootstrap themselves throughout the development process with literally only 3 people.