I had a similar issue when Uber was newer (I don't think they had XL) at SFO, the guy showed up in a little car, and was SHOCKED, SHOCKED, that we had LUGGAGE! At the AIRPORT!

He did not want that on his nice seat, and the trunk would not fit much either since he had his own stuff in there. Silly guy. He made us cancel, old trick, since that makes us pay not him. Support sorted it out.