Transport in beds

In real life I've never seen a patient getting transported on a stretcher when they are already admitted to a ward/bed. If they can't walk they would usually be transported in a wheelchair or in their bed.
Most patients can't even be transferred from a bed to a stretcher that easily. Same is for the trauma centers where it's often dangerous to move the patients too much.

So why not use the wheels on the hospital beds and trauma center/ER stretchers instead of having multiple stretchers that take up precious space on every ward?