That happened to my Mickii and Parry's Kaelii's Mom… her people decided it was too much trouble to take care of a senior (even if the sleep 90% of the time)... and we had to re-home her. What it really comes down to is they don't want to have to deal with death or having to maybe make the decision to help them over the rainbow bridge. Goods news was that Sadie lived another 2 1/2 yrs in a wonderful home before she went over the bridge
It's tough being the breeder or BRAT having to deal with something like this but you do because you're responsible. I would never ever of thought of getting rid of my previous three in their old age. They gave me a lot of joy over the years and getting rid of them at that point would have been an act of treason to the dog. I once told Karen at Medfy Basenji Rescue what's she's doing is impressive and she said no "it's depressing".