Because taunt has been the video gaming term for ages. Any game that has a button that allows an animation that doesn't do damage during gameplay is typically called a taunt and always has been, just how its been. To change it now because some people decided to take video game taunts to heart would be absolutely ridiculous. My view on it is....don't take it so serious
You seem uncomfortable with expressing the idea that 'taunts' are meant to egg on an opponent, which has often been the chief motivation for the mechanic's existence in the history of gaming. Considering your restraint to even mention that the word has negative connotations, I would think you'd be on board with suggestions for expanding the mechanic to something more positive.
The point is that it's not sportsmanlike to 'taunt' an opponent, either in real life or digitally. The word 'taunt', whether you like it or not, has always had inflammatory connotations, and clearly it resonates negatively with a broad swathe of the community if it still continues to dredge up arguments and debates amongst individuals. More importantly, for people with that sort of perspective on the terminology, a 'taunting' mechanic isn't very fitting for expressing things like congratulations or admiration. I've already seen on this forum a number of people mentioning how they like to think their taunts can express things like 'good luck' at the beginning of a match or 'well done' after having lost a stock, but with the mechanic being labeled a 'taunt' the meaning can easily be lost or mis-communicated. If the name was different, or if there were at least other ways for communicating different meanings made available in the game, those sorts of misunderstandings could be alleviated.
Wanting to return to the original Japanese meaning for the word is anything but ridiculous. Oftentimes people prefer translations to remain faithful to their original meaning. The fact that the game originally used neutral terminology to refer to the poses better captures the idea that they weren't necessarily meant to be taken negatively, in which case it stands to reason to use that sort of label since it's a better fit. If Nintendo had simply translated them as 'appeals' in the first place, I doubt we'd have a 'taunt'-supporting demographic up in arms that the company didn't follow an ill-fitting, negative tradition.
In any case, this thread is chiefly about expanding 'taunting' to other more positive forms of competitive expression. "Tradition" has never been a good reason for holding back improvements. You should offer a better reason than that for continuing to pigeonhole 'appeals' into negative terminology like 'taunting'.