Coulda just said, "They ruined it." I grew up on "The Alvin Show," which was all based on a funny Christmas tune made by a guy who discovered slow-speed recording. (A new thing back in the '50s/'60s.) He got his sped-up voices, that people said sounded like chipmunks, to harmonize. If he sang slowly enough, the tunes sounded like chipmunks singing in real time.
When it became a cartoon, Alvin's character was derived from the song: he was the non-conformist. And, like most kids, had to be cajoled into doing what he was supposed to. To flesh out his character a bit more, they made him clever; he was always the one thinking "outside the box," often outrageously. He also never missed the opportunity to tweak Dave, the perfect parent stand-in and straight man.
I'm seldom disappointed by anything that goes on too long. Seems to me that efforts to milk a great song, series or franchise usually ends up ruining it. I'm aghast at what Disney is doing to Star Wars. While Trek, so far, isn't completely into the weeds, I have mixed feelings about the J.J. Abrams stuff and can see ruin on the horizon. (Some might say it already happened.) They FUBAR'd the "Alien" franchise at movie #3. Back to cartoonland, I hated the "Johnny Quest" reboot. It had none of the charm and mystery of the original.
Of course, this is all my own opinion, and I'm no doubt horribly behind the times, having no kids and all. But Alvin I know.