No theory required:

> “I’m already building the best game I can,” said Mr. Roberts, who acknowledged the bumps. “But imagine — the game I can build with $140 million is going to be very different to the one I could build with $10 million. If I can build a bigger and more robust experience, I will.”

My guess is they keep going until donations taper off and they're about to run out of money, then rush out a massively buggy release that disappoints everybody.