Thoughts on the lack of adult human characters on Sesame Street?

[datman24]

Back when the humans were as valued as the Muppets, they made several book appearances, the vast majority of which were during the 1970s and '80s. However, by the 1990s, they pretty much stopped featuring them in books altogether, only making very rare appearances. To put it in hindsight, 19 of Maria's 21 book appearances were released between 1975-1991. In Alan's nearly three decades on the show, he's only made five book appearances.