I'm not sure why. It's not like the Disney sequels socking monkey dong magically made the prequels "better." Really it's just more material to poke fun at it, even if they were super-hyped that they'd be good. Hell, that makes it even funnier.
As much as I loathe the argument that "the Plinkett reviews are why Disney Star Wars sucks so much," there is at least a kernel of truth to it when viewed in the light of why they've been so soft on them. Mike basically got everything he asked for out of the Disney movies: no boring political maneuvering, no stoic and robotic Jedi, more fluid camera work, adventure stories, Rebels vs. Empire, even JJ Abrams directing. Even if Disney didn't literally use the reviews as a checklist while making their movies, they still did respond to various criticisms that had been levied at the prequels, no matter how fair they were (the most obvious being how they advertised all the practical effects they were using, when George used quite a bit in the prequels too). Thus, if Mike were correct in his assessment, then the Disney movies should have been a slam dunk, thus validating his critique.
And then they came out, and then everyone realized that just because you're doing something a different way, doesn't necessarily mean you're doing it
better, and that hack frauds will still make garbage even when they're trying to imitate good works. People were soft on TFA, even though it was a worse rehash of ANH, because they were hoping that Disney were simply use that as a way to reassure everyone that Star Wars was in good hands, and that they'd take things in a new direction later. They did, kind of, but then it just kept getting worse and worse, culminating in the absolute shitshow that was TROS. Now, Star Wars is a ruined brand that is still being headed by the retarded exec that put it in that state, with Lucasfilm reduced to creating forgettable streaming shows that exist solely to fill out Disney+ with content. No movies are being made despite close to a dozen being announced over the years, and a brand built on the toys it could sell now has barely any merch to speak of.
And yet, Mike can't bring himself to admit that maybe he was wrong, despite the proof being visible for everyone to see. He built his entire online reputation on skewering the prequels for their issues and essentially complaining that they weren't just the OT again. But when he was given what he said he wanted and it turned out to be even worse, he couldn't accept that he didn't have all the answers like he thought he did. Worse, people started to reappraise the prequels in a more favorable light as a result of Disney's mismanagement, effectively neutering his claim to fame as a bunch of pointless nitpicking. Thus, he kept his critiques of Disney to a minimum, unwilling to accept that anything could be worse than the movies he said were the worst things ever, doubling down any time people tried to get him to admit that the prequels weren't as bad.
Honestly, the prequels have their issues that probably should have been addressed in development, but they were clearly George's story that he wanted to tell. Disney produced nothing but memberberry slop that tore down everything that people loved about Star Wars. For someone that enjoys so-bad-it's-good movies, Mike is unwilling to admit in this case that an earnest failure is better than a cynical success, especially when the "failure" was rather successful and the "success" turned out shit in the long run.