I've said it before, and I will say it again: I don't really understand why. Machiavelli fucking lost. He spent a year in prison after the entire government he served was overthrown and then when he got out he gifted an ignored book to the new government. He isn't some evil super genius, he is a weird cuck who thinks being kind is a weakness. I have read The Prince, yes it is interesting. Clearly, though, the guy didn't have a complete philosophy. If he did, he wouldn't have spent so much time as a nobody.
Edit: Ultimately, being manipulative only works until people figure out that you are a manipulative asshole. You can't do it forever. I always roll my eyes when I see characters like Little Finger in Game of Thrones being shown off as some kind of bad ass political figures. Little Finger would've died way earlier, everyone knew the guy was shady and couldn't be trusted.