But in order to give access to someone with a
DAS, that would mean one other group (who waited in the queue) wouldn't get access. Unlike ride attractions, the characters that meet out in the parks (without FP+) have a limited time they can be out, by contract. So there's a set amount of guests they can meet - they usually cut off the line at a certain point. If they allowed DAS, the queue could be completely DAS guests, and guests without DAS would not have access. It's a first-come, first-served, very limited situation. They'd have to have a CM only accept DAS requests at a certain time, and you'd have to show up at exactly the right time, or else others would not get access either. So since that is pretty impossible, they really can't do more than allow one member to hold a space for the group. I guess they could do it like JTA and have a character sign up in the morning, but with all the characters out there, they'd have to limit how many you could sign up for, etc.
Think of it like the Cars ride at CA - the amount of people with GAC made it impossible for others to experience the attraction - the small group saturated the wait times and it was crazy.