After looking at that list, you can tell how important high school football is in Texas. It's like looking at a list of some of the high school stadiums in Western PA.
I've been to and played in some of those stadiums. The stands and in particular the locker rooms are pure sh!t. It would be a joke to have a MLS team in one of these crap stadiums.
And everyone said AAAAAAAAAmen!!! Not to mention that NONE of those stadiums had designers that factored in association football. Thus the field width is at best 68-69 yards wide. Noi bueno for MLS and FIFA standards.
You're right, smaller stadiums aren't everything. MLS experimented with Southlake and Naperville (heck even Spartan) and the LA/CLB SSS attendance boost effect was not there. At some level fans still have to believe it's a full fledge pro league.