They could give the ability to sponsor their own service with donations in the exact same way they do it for third party FOSS projects.

They're trying to solve the problem, not add to it.

If their solution is good, it should also be applicable to them

The difference being that this service has real tangible costs such as card fees for every transaction. That's not really comparable with "it would be nice to be paid for my time" when pushing your code to GitHub. I haven't used the site but it seems reasonable that one solution won't apply to all kinds of projects.

They could break out the transactions explicitly. That would help reduce the feeling that they're taking more than their share, if they're not doing that.

They could also sing a song, do a little dance and tweet a word of praise for your generosity.

At some point the dance isn't worth the peanut.

Well, if they're there to secure a good chunk of peanuts for themselves, for being the intermediator, many would find this shady and wont want to deal with them.

Sorry, someone donating $10,000 to their favorite FOSS doesn't want an intermediator to take in $500 just for making the transaction.

Even more so when the actual transaction infrastructure is not going to be their's anyway, but some banks or Stripe or whatever.

> Sorry, someone donating $10,000 to their favorite FOSS doesn't want an intermediator to take in $500 just for making the transaction.

This phrasing is just inappropriate, and the situation you cite is an extreme.

> many would find this shady and wont want to deal with them

What's the point of armchair prognostication? We'll find out, and their pricing isn't fixed in stone?

humble bundle suggests a tip and sliders with a 3 part system : what goes to the dev, what goes to charity, what goes to humble bundle.

Nothing stops you there to put 100% into one of those and 0% on the others.