Hamlin has a younger brother that was just born within the last year. He is extremely close to his family, so it's tough to leave them when he can literally stay home.
Also, there is a pull for the kids to stay home. Hamlin being from the actual city of Pittsburgh makes a difference. There is a LOT of pride from that city within their sports and Hamlin/Adams/Ford staying home is what the Pitt program needs to take the next step. Pitt is close to being a top team in the ACC, but the lack of consistent playmakers has hurt them in the aspect of reloading instead of rebuilding.
The coaching turnover at Pitt has definitely not helped, but I think Narduzzi will be there for a few years. And I mean Hamlin knows Narduzzi's track record with DBs and he rarely got a talent of Hamlin/Ford at Michigan State despite his success at the position. Notre Dame has a 1st year DB coach that is personable, but there is a blank spot on that part of Lyght's resume in terms of producing NFL talent.
While South Bend isn't far from Pittsburgh, it's still a five and half hour drive, versus the literal 5min drive from his high school to Pitt's campus.