ND is required to play 5 ACC teams a year. That alone gives ND more poll than 95% of their full-time members, as the ACC doesn't want to lose that. Stanford makes sense for ND football, it gives ND an opponent they'd love to play every year and now they "only" have to play 4 true ACC teams. If Florida State or Clemson leaves the ACC. That is a huge blow to ND's schedule.
ACC schools that are good for ND - Miami, Clemson, Florida State, and potentially Stanford
ACC schools that are decent for ND - Boston College, Georgia Tech, Pitt, Virginia Tech
ACC schools that are meh for ND - Louisville, North Carolina, NC State, Syracuse, Virginia, Wake Forest
ACC schools that suck for ND - Duke and potentially Cal