Mazzarri managed to get Napoli to 3rd place season before and was more experienced Serie A manager. Are you really suggesting that fans would have preferred Conte, whose only success till that date were two Serie B promotions? That's unreasonable.
Same goes for Guidolin.
The point is he wouldn't have been the first choice by most fans, whether they'd opt for Guidolin, Mazzarri, Donadoni, Allegri, Prandelli is another matter, but Conte clearly was percieved as another bad move.