Mainly because it was not Capcom's desire, the game was designed aiming another audience, just looking to the engine of choice and the game being developed to run at 30 FPS tells us a lot of things of how the mechanics would work out. Even if you make the game run at 60 FPS, it still was conceived and designed for running at 30 FPS, all the features were implemented along these foundations and design choices, you know?
A turbo mode would be good, but still has not much meaning for the game itself because it's more slow-paced (to welcome new players, i think) than previous DMC entries. It could still be enjoyable but would be just a "waste of time" by Capcom's and NT's point of view and purpose with DmC, Vergil in BP i think that was just lazyness from NT or greed from Capcom, i still think they will implement Vergil in BP officialy (and i think it has to be free, at least), but they need to rework the BP itself because Vergil can't tackle some monsters (it would be worse than fighting Nero's bosses with Dante). But if they had the game designed well in the first place, most of this would be possible, was just a little mistake that culminated on bigger things in the end.
Basicaly, the modding community for DmC see some potential in the game itself and try to bring back some lost features from old DMC entries to see if it works well with DmC. I have respect for people who actually work to upgrade a game they like, but i would not do this, i find it pointless because how the game was build and conceived do not match well some features and elements from previous entires. But props for the modding community who is making a good work into making the DmC experience better, i'll tell to my friend about all the mods and ask for him to download them for us to test some things.
The impression all this things leaves is that they're not quite certain with what to do with the game and the franchise, i think that relation of partnership from Capcom and NT suffocated NT's creativity and not achieved the same level of quality (gameplay-wise) of Capcom itself. They've reached a middle ground between this two things and the result of it is DmC.