No idea but if I had to guess... author got scared. BTC deposits were rocketing in just before the site went dark and he would probably have shot past the 1000BTC mark in hours rather than days if he'd have left it up. Running a public ponzi scheme that attracted over half a million dollars worth of deposits in a week with no signs of slowing down would have certainly given me sweaty palms :D

I feel it was technical scaling issues, probably from the sudden surge.

I say this because I received an absurd amount of BTC compared to what I put in (bare minimum, only a few cents) which would only have happened as a side effect of a technical issue.

Or they realised too late that they had a bug which caused some people to get back 900% instead of 120%. That would break the model. Underpaying is something you could correct retroactively, overpaying not so easy.

What makes you think it ended? People are still paying in and it appears to still be paying out.

I'm looking at the huge text on the home page saying "The experiment is over." If that can't be trusted, then why in the world would anyone expect to receive a payout at this point (as if it weren't already incredibly risky)?

I was seeing a cached version. Wonder why they chose to do it that way.