What accommodations do they have in place for guests with disabilities? Coach buses, with their steep entry stairs and narrow aisles, are unfriendly (at best) to those with mobility issues, and fully inaccessible to wheelchair users.
Presumably this would require also running some sort of paratransit shuttle along the same routes to accommodate guests who are unable to board a coach bus. Since shuttles have notoriously low capacity (1-2 parties per vehicle), this feels more like a temporary solution while occupancy is down, rather than a permanent one. At a certain ridership level, it just becomes easier to mainstream everybody into buses with level-boarding.