It looks like the team had made a Steam page for their fan game and were accepting donations for working on it, so I can see why Lego felt compelled to take it down. https://web.archive.org/web/20241125104301/https://masksofpo...
I don't see where you've read that they accepted donations. Every article and Reddit post I find says they didn't? It was indeed releasing on Steam for free, but I don't know if they had contacted LEGO before doing so.
Also, this wasn't the only Bionicle game that LEGO had endorsed, Quest for Mata Nui too, which makes this even more of a heel-turn. They won't have to shut down that one, though: the team went silent and then the main dev passed away.
Just last month LEGO shut down Masks of Power, the Bionicle fan game. They were really close to a release and LEGO had allegedly met the team and given them permission in the past.
I'm increasingly convinced that fan projects should be developed quietly and announced right on release, so they at least exist somewhere on the internet if they get shut down immediately after.