When Michigan State men's basketball became elite nationally, the school had to pay up to keep Tom Izzo and now in his 17th season, he's now the nation's highest paid coach but at about $3.5 million per year, he is well compensated amongst his peers.
In football, winning 22 games in two seasons obviously was going to make MSU's assistant coaches targets of other schools. And why shouldn't they look into any opportunity they have? Will MSU win 22 games the next two seasons? Maybe, but what if they don't? Then the market value drops. And if someone is willing to pay an assistant like Pat Narduzzi much more than he's currently making, well it's easy to understand why he is checking his options.
I don't know what his motivation in coaching is, but any coach is only as marketable as the team's last record and Michigan State at 22-5 the past two years has a pretty impressive record. In the past couple of years Mark Dantonio has lost Dan Enos and Don Treadwell to MAC head coaching jobs and it's possible now he may lose his second coordinator in two seasons. That usually only happens if a team is winning-- and winning big at that.