They very much do travel those distances to get to Happy Valley. I had a good friend who traveled from Kalamazoo (and Chicago when he live here) for weekends of PSU football as often as I took my 2 hour trip to ND as did his son until he moved to the west coast. The middle east coast is absolutely loaded with PSU folks. There always has been a dearth of decent college football on the east coast almost from Boston to The Carolinas which is why PSU used to own the middle atlantic re: recruiting. ND and PSU frequently recruited the same players from NY state, Penn. and NJ particularly.
Chicago may be close but you have multiple loyalties in Chicago ranging from Iowa, Michigan, Wisconsin, Indiana and it is loaded with Illinois/NW folks who for the most part don't really care for ND.
Yes I undercounted the South Bend area ..my bad.... but it still doesn't mitigate the sheer size of PSU as to why they can fill a 100,000 seat stadium and ND doesn't. And the fact remains that there are many times more PSU fans within a reasonable traveling distance to SC than there are ND fans to South Bend.