I did think about that after posting, But to be fair, he wasn’t alone on the cover. Big Bird was there with him, so it’s not just a minor character by himself carrying the release.
also, Forgetful Jones was more of a “core” Sesame Street Muppet than Little Chrissy and the Alphabeats. Even if the rerelease came after they stopped making new material with him and they were only occasionally showing him in the background (though they still showed old Forgetful Jones segments).
Though I wonder if they were careful about character selection or if the Sesame Street brand would have been enough to sell. I’d be really interested in seeing how well the original Random House release of Rock& Roll sold. Of course there have been Sesame Street books starting secondary or lower characters.
In thinking more about it, I wonder if it's best that the cover had Little Chrissy and the Alphabeats or if it should have been Little Jerry and the Monotones. Little Chrissy is featured in two back to back songs, while Little Jerry does have a bit of a plotline in this. Still, by 1990 I think Little Jerry and the Monotones were a bit obscure. While not really major, I was more aware of Little Chrissy and the Alphabeats at the time, don't think I was really aware of the Monotones (aside from noticing Big Jeffy in the background in A Muppet Family Christmas). Still, as a Sesame Street fan, I probably wouldn't have cared who was on the cover or if I was familiar with whatever Muppets were on the cover. Of course I never had that one until it came to DVD, though it was one of the Sesame Street videos that I really wanted at the time (mostly for some of the songs listed on the back).