How often do big name, successful managers go to smaller clubs? Does anyone legitimately think Mourinho will end up at Aston Villa or Palermo if he leaves Real Madrid? Or if Mancini leaves City, he would end up at Sampdoria or Siena? World class managers, proven at the highest levels with trophy hauls, rarely end up at smaller clubs. Not impossible, but uncommon.
A club like Ajax would be a poor fit for a manager like Guardiola. They have a very set vision for the club - tactically and in-regard to personnel. Although the Ajax youth system bears some similarities to the Barcelona cantina system, there are also some differences. Not to mention that Ajax is, fundamentally, a selling club. Most smaller clubs are, at the end of they day. But at Ajax, its basically become part of the identity.