Ultimately, the money theymos spent on this project was his own. The money he received from donations were reasonably his when he received them. However, even if this was not the case, he only received approximately $70k in donations, denominated in BTC. He made the decision to not convert the BTC to fiat, and as a result, saw massive capital gains.

So I guess the answer to your question is that theymos is a millionaire who has wayyy more money than he knows what to do with.

I also don't think $400k for a developer is unreasonable. Especially considering the potential for the project to end at any time, even if it lasted for 10+ years. Slickage obviously needed to make a profit, so not all of that money went to the developers, but most of it probably did.

The project failed, which, unfortunately, is not uncommon in software development. Could things have been handled differently? Yes, hindsight is 20/20. Meta spent billions on the "metaverse" in about 20% of the time, and that has been pretty much abandoned.