As Taylor said, maple is simply the best of the timber sized woods that grew in the U.S. Sugar maple and most red is hard, dense, stable, diffuse porous (no large pores in the spring wood), carves well and often blessed with attractive grain.
There is also fashion to consider. Gunsmiths in New England seem to have preferred cherry and walnut despite living in sugar maple country. I've always found that odd because New England made furniture is often curly maple. Go figure!
European walnut, which is also an excellent stock wood, was not readily available here and fruit woods like pear rarely reach the size to make wide boards for cutting long rifle blanks.
Maple has been the wood of choice for bowling allies and basketball courts for years and recently it has replaced ash as the wood for professional baseball bats. Same list of reasons--hard, stable, etc.
Gary