No. It's much like the music business: they need new PewDiePies, though it's cumbersome to create them. Once you're PewDiePie for a while, you have more resources and access to lawyers and managers, and you come around looking for a better deal.

From YouTube's point of view, that's bad, so they need a replacement. It's quantity of views they need, they don't actually have a stake in the success of any one creator.

Is it possibly because you're a nerd, and the internet is no longer for nerds? It's now a platform for mass consumerism, and what interests the masses, and is thus good for advertisers probably shares little overlap with your interests?

It is likely that PewDiePie has a negative enough image that YouTube believes that associating a given brand with his content will not generate ROI for the advertisers. By demonetizing these videos 1) the advertisers win because their ads are shown more frequently in "profitable" spots, 2) YouTube wins because they build trust with their advertisers, and 3) YouTube wins again because they don't have to pay out to the content creator for valueless ad spots.