I think it's because of the radical changes that were made to a franchise near and dear to many peoples hearts. It might have seemed a bit sudden and not planned out. My initial reaction was a "YES", mainly because I felt a strange sense of dejavu while I was playing DMC4, not with the story but with the all too familiar gameplay, the repetitious nature of the game design, the bland puzzles, and the similarity to DMC3 (not that DMC3 was bad, I just expected a bit more from DMC's first next gen iteration). DMC4 was a good game you had to play through twice, artificially lengthening the game since you were basically playing the whole Nero levels, only this time as Dante.
After DMC4, I expected Capcom to make some major changes but I wasn't expecting a reboot at all. When I saw the debut trailer though I was very surprised and enthused. So its safe to say I was up with the reboot idea from the start mainly because I want a fresh take on my favorite franchise. And really, so far, its looking pretty good (to me at least).