(literally zero reason to call them trigger warnings other than to signal tribe allegiance)
Because that's what they are called...
There is literally zero reason not to call them trigger warnings other than to signal tribe allegiance. It's the classic "people of groups I'm not a member of are so cliquish, why is only my group neutral?"
When consciously making a change from what is currently used, the implication is that what is new is better or more accurate in some way. Changing the word from "content" to "trigger" isn't about clarity or better description, it's about an agenda (probably already rolling your eyes, but hear me out). In this case, the agenda to me seems to be about getting the word trigger into mainstream acceptance, whereas it's currently widely ridiculed. Whether the word "trigger" has a more specific meaning more free of connotation in psychology I don't know, but I do know for most people it has very strong connotations with the whole SJWs on tumblr thing, LW's crusade against purple-haired women, etc.
I don't mean agenda in a derogatory sense. Everybody has an agenda, and I'm pushing one right now by putting making this argument. The point is that I think it's reasonable to oppose the replacement of neutral and functional words with words whose connotations suggest an agenda or political alignment, regardless of the agenda or political alignment in question. It sounds trivial, but language is a powerful thing, and these sort of subtle manipulations of vocabulary are not an ethical way of supporting a position in good faith.
In this case, the position being supported is trivial and I really don't give a shit what people use, but I don't think it's right to dismiss people's objections as tribalism and pigheadedness.