Well, ISU has orientation in June, and all the incoming frosh that I personnally know bought there tickets then. That first part caught my eye though. If students don't have that spare $125 by July, what convinces you they'll have it in August? Especially since you can charge your U-Bill and not pay until September.
Right now, a lot of them are pretty busy with summer work and such and don't have enough money.
Also, a lot of incoming frosh will probably wait until they either go through orientation and get their student ID number or wait until they move in and do it when they have nothing to do.
They AD has been reminding returning students about getting their season tickets since April, and there's a season ticket "stand" in Beardshear every summer for incoming freshman to learn about, and buy, season tickets while they're there getting their ISU card and whatever else it is that's set up there for orientation.
I have received emails from JP during the summer to get season tickets. But, that may be because I was a returning student who had purchased season tickets the prior season. As for incoming freshman, I'm not sure if they received those emails or not. If they didn't, they probably wouldn't be exposed to any marketing for season tickets, until they get to Ames