All software has bugs in it.

People were using this service to put up money to encourage programmers working on open-source software to fix specific bugs that were especially bothering them. For instance, if text in software X didn’t scale properly and that was a problem for you, you could use this service to offer $100 to programmers working on X to fix the text scaling. Once they got it fixed, they collected the money.

The service went bankrupt.

When it went bankrupt, some programmers didn’t get their promised payment for bugs they had fixed.

The money didn’t get returned to the people who had paid for the bug to be fixed, either.

So now both programmers and users have lost money because of this service, and everyone’s ticked off.

Many popular foss apps use Open collective

Bountysource was owned by a company called The Blockchain Group and it looks like the parent company went bankrupt taking Bountysource down with them. Its hard to say if Bountysource could have survived if it wasn’t sold to some cryptocurrency companies.