Executives on most NFL teams do not have the trust and confidence from ownership that we are used to seeing with the Patriots. That means the career of a general manger or whoever makes personnel decisions is very closely tied to his choices, more so at quarterback than at any other position. That leads to taking the safe route, which would be to draft a rookie - a route that also buys the GM and HC more time.
Going with a veteran QB is riskier because it is more likely to be second guessed, with comparisons to players from Matt Flynn to Scott Mitchell. They will be expected to produce right away, and the problem is that most teams that need a new quarterback probably also need upgrades at other positions before becoming a playoff contender. Another losing season and the GM and HC are on the hot seat, the new QB becomes the scapegoat of fans and local sports talk radio, and confidence dwindles.
I think Mallett will receive offers where he can compete for a starting position, but I don't expect him to be given a big payday.