In the decade or so I've been playing MET, I've found that most social challenges tend to make *players* angrier than most non-fatal physical challenges.
Damage is something most gamers are used to in most games. Sometimes you take it, sometimes you die. In a game where wounds take a long time to heal, damage might be a Thing, but in Werewolf, damage tends to evaporate within 30 seconds of combat ending. So if you surprise someone with a physical challenge and they take some damage they can trivially regenerate, they're likely to shrug it off unless they don't have anything better to do.
The part of the game you have absolute control over is who your character is, what they think, how they react emotionally. That's also the part of the game people tend to be the most invested in. Trying to change how someone plays their character with a social challenge goes right up most player's asses, because you're reaching into the internal narrative in their head and rewriting it violating their free will.
I have two favorite examples of this. One is how often I see players lose all their rage to Calm or something like it and then say "hey, I just lost a bunch of important stuff, can I gain a Rage?" This makes perfect sense if the formula is player dislikes a thing->gain a Rage, but no sense if you look at it as "my character just got less angry... and this makes them ANGRY!" (Exception: You are playing The Hulk.) The other is when I tried to play a Ragabash with more social traits than anyone else in that (non-org) game, where the entire idea was "I say this thing a Ragabash needs to say, but I have so many social traits that your PC is not offended by it at all and actually listens to it," and this failed utterly. Players routinely spent willpower (which was a precious resource in that game) to retest my social challenge in which my only goal was "you're not really bothered by that when my character says it."
We could remove the option to cancel giftless challenges with a willpower. IME, most players that I've ever larped with will find a way to ignore those things anyway - by either just ignoring them completely, or playing them reluctantly, or immediately having a friendly PC challenge them back into thinking whatever they wanted to think in the first place. I'm not convinced they're entirely wrong to do so, either.
If I thought there was support for it, I'd put up a poll with options for leave as-is/WP to retest only/2WP required to cancel/you may retest WP when defending a giftless social as many times as you like until you run out, but I generally get the idea that most people who are not Vance or Rick prefer it exactly as it is.