The DME buses don't all have buses. You should tell them when you make your reservation that you need a wheelchair accessible bus. That will make the shortest wait. Each wheelchair bus can hold up to 2 wheelchairs.
Almost 100% of the resort buses are wheelchair accessible and can hold up to 2 wheelchairs or
ECVs in the wheelchair tiedown spots. There are a couple of possibilities for the bus leaving a stop without loading a wheelchair.
1) There may have been wheelchairs or ECVs in the spots, but the people using them might have been sitting in bus seats instead of in the wheelchair, so it may have looked like the spots were vacant.
2) There may have been one wheelchair already in the spot closest to the door - that would have left the other spot empty, but it may not have been accessible because of the size of the wheelchair already in the bus. That has happened to us once or twice. It also happened to someone else when DD's wheelchair was secured in the spot closest to the door and a man with a heavy duty
ECV was at the next stop - he would not have fit in the bus unless DD's wheelchair was removed so he could get by.
3) The lift or tiedowns might have had something wrong with them that made them unusable. That has happened to us a couple of times. On one trip, the driver tried to attach the tiedowns, but something was missing, so we had to get off of the bus. Because his tiedowns had a problem, he would not have been able to pick up someone at the next stop. On our last trip, the driver could not get the lift to come down correctly for us, so she would not have even tried to pick up a wheelchair at the next stop.
4) The drive may not have seen that they wanted to go on the bus. That's especially possible at the resorts, where buses for multiple locations come to the same stop.
If the bus is full for wheelchairs (the lift or tiedowns don't work or the spots are full) and there is a wheelchair to load, the driver is actually not supposed to pick up any passengers at
that stop. They can continue to pick people up at the next stop.