D23 they do all of the live action films in a 3 hour panel. In 2015, Force Awakens had all of 15 minutes, and I think only 4 of the stars were there (Daisy Ridley, John Boyega, Harrison Ford, and Lupito N'uyongo). Much smaller than their SDCC panel. They might not want to bring everyone for Infinity Wars in for such a brief appearance.
I just haven't gotten the sense that D23 does the 10+ person panels like we've seen at SDCC.