One of the many hats I wear is that I'm on the veterans liaison committee for the Perley Rideau, and this situation arose. I think one of the things we must differentiate between is hospitals and long-term care.
I know in some long-term care facilities the wife can share a room, but in others they can't.
Honestly, as to why and why not...I do know we had a case at the Perley of an air force veteran whose wife's presence was refused at first, but later on they relented and she did share a room with him. Further than that, I couldn't say.
You might like to get in touch with Cliff Chadderton at War Amps. I think they could answer that one.