Petersen's staff is not elite (hard to keep top shelf guys at BSU). So he is going to add some new blood. Most coaches are under contract somewhere else, have loyalties to other coaches/programs, etc. So it is complicated getting them to defect to a new staff.
Compare this to Tosh. Well known to be one of the best recruiters in the country. Also widely regarded as a d coach (Sark is a mediocre coach, but he's not stupid. There is a reason Lupoi has an offer while cozzetto and kiesau are checking their 401ks).
Tosh is gift wrapped for Petersen. Under contract w/ a sizable buyout. From all accounts, he likes it here. Also has a reputation as a mercenary that he probably wants to downplay. Coach Pete should make this happen.