Can’t any donation platform you don’t fully control cut you off at any point?

What exactly is different about GitHub sponsors here?

In theory sure, but you have to evaluate how likely it is.

Some typical dynamics:

Big org platform -> exposed to risk, as you are not a significant addition to their bottom line

Small donation platform -> Can be easily bullied by payment processors to "derisk"

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every.org is a bit special, as it only lists 501c nonprofits - which the Zig Foundation is - and AFAIK has a decent track record. Most other open source projects don't clear that bar.