Tony Romo starts a game for the Cowboys in 2017 than Bonzie leaving ND a year early.
His family wants him to get his degree and there is no money issue with his family to my knowledge.
His stock will not improve or dip by staying. He's going to be a second round pick at best (who probably will have to play pro ball overseas). He enjoys being a college kid.
College players returning for senior seasons usually hurts their stock (the lure of upside is diminished). In terms of DJ, he was also worried that the 2017 was heralded as being loaded with high upside one and done point guards. He was right. Joel Berry has to factor this for his decision.