Doesn't ASU have one of the largest enrollments in the country? They are like 3 times the size of ISU. I'm sure they have a ton of alumni everywhere, including Texas.
They're massive but it's also a little misleading. Their president (an ISU grad) has been super aggressive in expanding their reach through online classes, partnering with companies like Starbucks to offer free undergraduate education to their employees, stuff like that.
Which is not to say those students don't count, just that they are less likely to have an affinity for the university (and do things like attend football games) than students who have the traditional undergraduate on-campus experience.
That said, even after accounting for that, ASU is quite a bit bigger than ISU enrollment-wise so I assume they are in alumni base as well.