Because most people who run a kickstarter for a small company aren't project managers. I know how this stuff works because I am one, and have run many projects in the past. I know how easy it is to fuck up your scoping or milestones and how easy it is to slip right on dates due to unforeseen difficulty.
There are some examples of successful kickstarters who managed their projects well and kept the development within the scope they could handle. Not a lot, but there are some.
I still firmly believe, as Ventus says, this project spiraled out of control. I think he started off with a simple prototype that had most of the initial features working decently but the stretch goals required some major refactoring.
They started out with hand-drawn maps and predesigned levels and tried to end up with infinite procedural possibilities. That is more than a refactor, it should have been a sequel if anything, with a larger team than 'one guy' working on it. One man working in isolation is susceptible to all sorts of roadblocks that can stymie work and bring progress to a crashing halt indefinitely. He'll have no emotional support, no oversight, no help with difficulties, etc. It takes a toll on you, and you can get to a point where you are just exhausted and no longer WANT to work on your project. And once you get there, its hard to do anything productive. This is one reason people work in teams.