It was partly because the grown-ups on Sesame Street kind of freaked me out. They were overly friendly and it also seemed to me that they talked down to the puppets. Also, it used to make me cry because no one would ever believe that Snuffleupagus existed, even though he'd just been RIGHT THERE.
On the Muppets, there was a far more sensible person-to-puppet ratio and less of an emphasis on counting. There was only one problem with the show: it featured a terrifying creature who, because Darth Vader had already claimed my bedroom closet, got into the habit of materializing on my wall. This horrifying, terrifying, sinister Muppet was named Uncle Deadly and he was the Phantom of the Muppet Show.
It's funny how impressionable and malleable and defenseless and hysterical a kid's mind is; he seems to have appeared on the show only a couple of times, and yet he had enough of an impact on me that he carved out a piece of the nightmare part of my brain for his own.
He turned up first in the company of Vincent Price, who scared me. He then turned up again singing with Ethel Merman, who also undoubtedly scared me.
He appeared to various muppets, and scared them, and Kermit thought they'd imagined it all (WHY ARE MUPPETS SO FAITHLESS AND SKEPTICAL?!?), but finally he saw Uncle Deadly for himself and learned that Uncle Deadly used to perform at the Muppet Theatre as Othello before he was killed by critics.
I'm sure that episode ended with Deadly becoming friends with everyone and turning out to be a loving and supportive friend, but I blocked that part out. When he turned up on my wall (his eyes would glow - I could actually see his eyes glowing), he was not friendly. I don't know why I didn't just set Darth Vader on him.