For example, how would I know if my mouse driver software happens to use a certain Node module, and one of its auto-updates just starts breaking things? Yes, it would be a stupid technical decision on the part of the mouse driver company (and that company would ultimately be responsible for the fallout) but how does that help the person actually affected, in the meantime? And did the protestware developer really not think that someone “downstream” like this could be affected by such decisions? Not everyone is sitting at a terminal seeing a message printed out.
Of course there are other reasons too, e.g. you completely destroy your credibility as a project (or even potential employee in the industry) by pulling stunts like this, and how could that be worth it in the long run?