Priorities change. Running was mostly just a college application activity in high school. Then in college people realize everyone out there in ncaa is fairly good runner (compared to HS where there were tons o JV runners to beat) and it’s harder to stand out unless you’re really really good aka not terrible by LetsRun stAndards . Plus women and beer.
In high school a lot of slower runners make you look like an amazing runner. In college everyone is an amazing runner (relatively speaking)