My experience is different thenI live in Northeast Kansas, right along the Kansas/Missouri border. Besides Oregon, I haven't really noticed another team taking foothold here besides the locals. If anything, I think our interest here has grown. Another thing that I believe can contribute to kids wearing other teams apparel is the "gear sales". Some of my friends used to go to them when was in high school a few yeas ago. Basically you pick up a teams cool, catchy gear for cheap. Most kids nowadays don't really care who the university is as long as they look athletic and cool wearing it.
Ive also attended some Nike Combines and FBU camps in other parts of the country
I found the same there- lots of team gear from other areas of the country.
It varies a bit by region
Damon Benning was on the radio today- he said he saw the very same thing I did
His sons three favorite teams are NU Oregon and TCU- has gear for all
One of my own kids likes Lacrosse and wears the Duke gear- a great Lacrosse power.