If colleges, especially the dorms, are a big risk, hotspots would have occurred long before now. US colleges have a very high number of international students especially from China and Europe, and a high % of international travel and exchange.
In addition, colleges are cramped and crowded. Extreme density on campus, in dorms, houses and apartments to save money. Colleges should have been THE hotspots, the hardest hit of all.
America is aging which Covid has made painfully clear. Many college students have older parents and especially grandparents. If college students are Covid vectors or conduits, the pathway would have been very clear by now with easily traceable hospitalizations or worse.