there are limited seats for the band that each school has to allot and that's where Bama wanted to seat them.
Also, MSU has put other school's band in the upper deck before. I know that we've done that to Ole Miss twice. I can't remember, but we may have done that to Bama to, and they wanted "payback".
The crappiest thing that I've ever seen another school do to the FMB was LSU in 1998. We brought the whole band and they made us leave our seats after the first quarter and made us sit under the stadium until there were about five minutes left in the second.