Because the description is about asking questions or making requests that would otherwise be insulting to the one being questioned, not deescalating tense situations. It's not really in the spirit of the Trick based on a plain reading. Excepting some instances, in the general case I don't think you would characterise "Hey let's not stab each other?" as an insulting request to begin with.
Clicking through that reply to what was being asked (thanks for finding it!), I see it was about Tricks to signal peaceable intentions or keep a bunch of Vikings in order, which yeah, don't really feel like well defined Tricks. But I don't think either of those are the same as deescalating tense standoffs, which feels like a logical extension of Silver-Tongued, so I think I'll check.
Hey,
@Imperial Fister, could we develop a Silver-Tongue trick for helping us when trying to deescalate tense situations or standoffs that are on the brink of violence?