Because it's no longer 2008, and his Nostalgia Critic schtick wasn't any good even back then. Hell, the "critic with a gimmick" thing is super outdated by now.
Doug actually has a series called "Doug Reviews" where he reviews movies without the Nostalgia Critic persona. It doesn't get as many views.
Nostalgia Critic:
Wonder Woman - 334,000 and climbing
Transformers non-review - 555,000
Alien vs Predator - 782,000
Suicide Squad - 1,179,000
Flintstones 2 - 829,000
Clockstoppers - 739,000
Fan4stic - 1,079,000
Doug Reviews:
It Comes at Night - 96,000
Power Rangers - 276,000
Get Out - 114,000
Split - 191,000
Could also look at Sibling Rivalry (where Doug and Rob Walker team up to talk about movies):
Wonder Woman - 173,000
Guardians of the Galaxy 2 - 180,000
Beauty and the Beast - 324,000
Logan - 194,000
Fifty Shades Darker - 251,000
Rogue One - 196,000
Doug seriously tried to get rid of Nostalgia Critic back when this thread was created in 2012, but Nostalgia Critic is the one that puts food on his table.