Do people even think about the horse's hearing?

They actually have equine earplugs.

I know but i have rarely see people use them and there aren't any studies to see how effective they are, also the horses don't like them so its hard to put them on so many riders just don't care and not use them at all. Maybe this horse does have them but still kinda bothers me to see the muzzle blast so close to their ears, when your head is that close to a muzzle blast ear plugs have to fit perfectly or else you still get ear damage and the equine ear canal is different from a human so i think is better to take care about their hearing even with plugs, its just a show after all, no life or death situation.