It would have been interesting to hear why. When I visited with D19 (in what was a much bigger audience than the one you described) they said something like they had their own app because they wanted to know people really wanted to apply there and would put the effort into it, rather than just ticking another box and adding supplemental essays onto the common app.
FWIW, D19 also found the pre-professional vibe off-putting.
(Edit to add, this is for Georgetown)