It's not because they're "immature" or anything like that, and it's not a diss on anyone who still likes them, it's just that I tried to watch a new video of theirs and it just didn't hit me like it used to.
It's similar to what happened with me and the Nostalgia Critic (Tho admittedly with significant differences): I was a pretty big fan early on and for several years, but over time just fell off, started watching them more sporadically, before kinda just not keeping up with the new stuff anymore.
I've had similar feelings. The last series they did that I enjoyed was the Danganronpa one. I think the fact that they keep playing these fucking boring-ass game-show games is also turning me off. Part of me feels like neither of them really want to do it any more, but don't want to give up the gravy train (fair enough). I wish they'd do more multi-part series again, maybe play some whole games, etc.