The candidates chose not to campaign in FL & MI in order to appease those four states.
Nonsense. The candidates didn't sign those pledges to "appease" the small states. They signed those pledges because the DNC - by stripping FL and MI - gave them no reason not to. The candidates wouldn't have hesitated to campaign in FL and MI if those states hadn't been stripped of their delegations, the "four state pledge" be damned. Even with halved delegations, Michigan and Florida would still have been among the biggest prizes pre-Super Tuesday.
Well, OK, that is sort of what I meant, but perhaps I could have explained it better. You said "It did, however, secure from the candidates a pledge to not campaign or participate....", which is not really correct, as the DNC didn't secure that pledge. The DNC did *enable* that pledge by stripping the delegates. And yes, if they hadn't stripped the delegates, then the candidates would never have gone along with the four state pledge.
But if it wasn't for IA/NH/NV/SC demanding the candidates' loyalty, I think there still would have been some campaigning in FL & MI, at least by Clinton. True, no delegates, but if she thought she was going to win them, and she wasn't constrained by any promises to ignore those contests, she would have still made some kind of effort there, in order to make them seem important, so as to get some kind of momentum boost. Same reason why so many candidates spend so much money on the Iowa straw poll, even though it awards zero delegates.