> Machiavelli's dislike of mercenaries was poorly placed, as after all they were simply following the economic incentives.

That is part of the reason he did not like them, their loyalty was bought and the "prince" who used them did not have any other leverage. It is difficult to win and then govern with mercenaries as the protectors of the kingdom. A long standing mercenary army does not convey legitimacy, and when disbanded there are issues of proper resettlement and worry about a rival acquiring their service.