Sesame street was considerably funkier, psychedelic and kind of gritty. Elmo was a herald of a much cleaner and sort of infantilized Sesame Street. The massive commercial success of the Elmo toys especially made it feel like it had become very commercial and a lot less grassroots.
https://www.youtube.com/watch?v=_ul7X5js1vE
https://www.youtube.com/watch?v=jwio5qGg8o4