Donations are not allowed because the original developer KovuLKD didn't want his game to be funded by it.
This makes me curious; how do you know that? The game and none of its assets come with any kind of license document, so I find it difficult to be certain what any one of the author's wishes really are (excluding dynamic linked libraries here). My guess why donations are not taken is because of that very problem (lack of license), so staff assume that all rights are reserved (a safe bet), OR irrKlang's ambiguous non-commercial license persuades them to play it safe.
Why do every single one of you love to miss the point? Let me restate:
The game is not going to be funded, the servers can be. The servers are separate from the game. The donations, in theory, would not be to create new assets, or edit the code. Just support the servers. (And to hep out our beloved Razmirz)
It is maybe counter-intuitive to think that donations can violate a non-commercial license (assuming here FeralHeart is under some variant of that, see question above). It can be seen as a form of indirect financial gain, unfortunately, since the donation button would likely be placed somewhere on this website, a website for FeralHeart.
Disclaimer; I'm not a lawyer, but that's the general gist I get of the situation and why you probably won't be seeing a donation button here any time soon.