Well, I did notice that out of the 100+ episodes available, some segments were only seen on just one episode, such as "D-Dart" and "V for Vitamins" to name two. They likely only wanted to pay royalties for just one occurrence of such segments. Some segments, such as the snowman poem, was released more than once though.
I did notice, in the second batch of fresh classics last December, there were some segments that were not seen among the original batch from May 27, 2020. They include "T for toys, teacher, turtles with brains, etc.", "Scanimate H", "Riding on the Train", and "J for Jack-in-the-Box" (the latter with Gary Owens' voice).
That said, I think it's pretty likely that there may be no more fresh classics for quite some time (at least), as there are very few classic segments remaining that were never shown among the 100+ episodes existing on HBO Max.