I’d guess it’s because they aren’t saying “all motorcyclists have a 1 in 722 chance of dying riding a motorcycle” they are saying “1 in 722 Americans will die in a motorcycle crash” while completely disregarding that only (making this number up) 80 of those 722 ever even rode motorcycles in the first place.

In other words, pedestrian deaths simply outnumber fatal motorcycle accidents because there are a lot more pedestrians than motorcyclists.