I think you’re getting tripped on definitions. It seems that paleontologists have adopted a new convention in their definitions and illustrations, and we have to “adapt” (hah!) to that convention.
A series of transitional fossils demonstrates the history of transitions that have occurred. A transitional form is not necessarily a direct ancestor of a modern form; it might be, but it might also be the “cousin” of as-yet undiscovered contemporaries that were on the direct line to modernity. Those as-yet undiscovered cousins would be roughly similar to the discovered cousins.
The first time I saw this convention used in a cetacean evolution diagram, it stunned me for a minute. Then I realized that the paleontologists were trying to distinguish between what’s highly certain (the general path of the transitions) and what’s less certain (the exact placement of fossil species on the tree), and I appreciated the effort. Of course, the risk is that the new convention might lead to confusion amongst folks who did not learn this kind of diagram during their education.
The other source of confusion might lie in the way that the Homo group is depicted. I believe that a “group” was chosen rather than branches with leaves because we know from genetic evidence that various members of the different Homo species mated. So it’s not that no transitional form exists; rather, the transitions do not have sharply defined boundaries.
Yeah, I’m having a hard time keeping up. Hopefully this post is mostly in agreement with what anthopologists have figured out. I invite any experts in the field to correct anything I might have missed or misportrayed.