A couple of things have happened since my time actually in the Gopher Athletics Bands, so bear with me.
At Minnesota, the pep bands -- and there are three for winter sports (plus volleyball) -- are operated by the School of Music with funding from the Athletic Department. The funding is based on a certain amount per band member per event. The third band was added shortly after women's hockey became a varsity sport because there were too many requests for coverage from just the two existing bands. My understanding -- and this may be completely incorrect, so apologies if that's the case -- is that Wisconsin only has a single winter pep band; that could be due to funding, that could be due to staffing (i.e. directors), or it could be due to another difference in the operating model.
But even if everything else is ideal with no limits to funding or staffing, having only a single pep band limits the number of events which can be covered; the band members are students, too, so the time commitment comes into play. For some instruments, there are physical limitations, too, to how much playing can be done in a certain amount of time (the chops of trumpet players is typically limited).
Just a few thoughts.