I'm just the opposite. I prefer fresh, raw onion on burgers. I do NOT like them cooked/sautéed.
(onions are fine in recipes, I'm talking about burgers)
Even on a patty melt, where it's traditional to have sautéed onions, I prefer them sliced and raw.
In-n-Out offers their customers the choice...because not everyone wants onion breath...not everyone LIKES onions, and it's just good customer service.
No...it's just good math. They probably get less complaints by asking if people want onions (and or save money) vs putting in raw onions by default.