I think y'all are confusing field hunters with show hunters.
Running martingales are illegal in the show hunter ring, regardless of how common they are in the hunt field, the jumper ring or that they're prefered by eventers.
Both types of martingale are common and accepted in field hunters, though the standing *might* be considered more traditional.
It helps if you recognize that logic doesn't have a lot to do with this.
I personally don't feel that there's anything unsafe about a standing martingale, particularly when jumping stadium type fences in cups. The eventer's argument is that it a horse becomes entangled in a solid fence, that the standing martingale somehow inhibits whatever heroic balancing gestures the horse would make to extricate itself. However, fox hunters jump formidable obstacles in unpredictable footing and uneven terrain, so you would think they would have the same bias, but they don't. Standings are common in the hunt field. Also, eventers also are not allowed to use standings in the stadium phase, which doesn't make sense, as the fences are in standards and cups, but there you go.
FWIW, standing martingales are somewhat of a fashion accessory in hunter ring, because someone somewhere once decided it "dressed up" the horse. A horse that *needs* a standing martingale (It's only purpose is to prevent the horse from raising it's head above the effective range of the bit) probably isn't going to do well in a hunter class anyway.
They're overused, and too many horses learn to use them as a crutch and brace down on them in the turns.