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.
The grunps are hit or miss. I have met them at events are they are exactly the kinda people you meet at your local boardgame meetup only they are millionairs about it so it is a weird vibe.
The videos are good sometimes and othertomes they are just making weird noises at the camera