I have often heard many friends, relatives & people here on the Dis say they (non-disabled) were put into a HA Room with a roll in shower! Why are people who did not request a HA room at all being placed in the few rooms that are available for those with special needs? I have asked these people who put into HA rooms if they asked for a room change. More often than not they didn't want to take the time, since the room was still okay for them.
There is a grid that is part of the ADA requirements for hotels which details how many handicapped accessible rooms are needed per 100 hotel rooms.
I can't post it as a table, but it amounts to about 5 handicapped accessible rooms per 100 hotel rooms. About 4% of the rooms have to meet the guideline for handicapped accessible (which involves amount of room in the bathroom, grab bars, etc). About 1% of the rooms need to be fully accessible, with a roll in shower, grab bars, fold down shower seat, etc.
I don't know exactly how many rooms WDW resorts have in each category, but from what I have been able to find out over the years, they have more in each category than they are required to.
When people who need an accessible room make their reservation, a room is arranged for and blocked for them ahead of time.
A few days before people arrive the room assigner starts assigning rooms. Any handicapped accessible rooms that were not pre-assigned are left in the general number of rooms that can be assigned.
CMs who work as room assigners have posted that some of those rooms are typically left empty in case someone requests one at check in, but the majority of them are just assigned to people.
That would be how the people that you are writing about got those rooms - because there was no on at the time requesting one.
Our family of three non-disabled people had a room with a roll in shower at Pop last Feb. I guess maybe it was because we had requested a king bed at check in.
It did have a king bed, but also the wheelchair bathroom. We weren't crazy about it because it caused a big flood every time we used the shower and the toilet was much higer off the ground, a problem for our three year old. We didn't ask to move, though, because it wasn't that big of a deal and we liked the room location.
You are probably correct that you ended up with the roll in shower room because you requested a king bed.
Many people who don't need the accessability actually ask
not to have a roll in shower room because they don't like the higher seat toilet, the lack of counter space and the roll in shower.