People should stop exploring new ideas the second they graduate college??

Sounds like a sad way to live.

Should they? No. It is their life to live as they please. Imparting your expectations on them is of no use.

Will they? Generally, yes. Work, kids, partners, home maintenance, etc. tend to take priority once one becomes an "adult". There is only so much time in the day. That is, after all, why one seeks to front load their remaining life's idea exploration by going to college. Those who plan to explore ideas for the rest of their life simply do so. They don't need "hallowed halls".