It does make me sad to see dogs rehomed for many reasons. Some I can understand, but some, like "I just don't want them anymore" make me so sad for the poor dog.
It is SO much worse though for people to NOT rehome a dog....for whatever reason...when it would clearly be in it's best interest.
I am currently trying to convince a couple who live near my parents to give up their 6 mo old yorkie boy. The got him, not
really wanting him to begin with...or such is the impression I get. They'd been trying to adopt a baby for a while, but 'settled' for a dog instead. Shortly after getting him, they found out they were going to get their child and are awaiting it's arrival, which has put the 'second choice' pooch to the side. I don't think they have even tried to house trian him yet.

I am trying to convince them to let me try to find him a home, but they are insistant upon letting me 'buy him' from them so they aren't 'out the money' for him.

I can't keep him and am not prepared to pay what they are wanting for him.
Anyway, in such a case, I would MUCH rather see him rehomed than not.

As many people as you see who so desperately want a Yorkie, but don't want to pay more than XXX amount for them, seems like this would be a perfect fit. (And yes, I realize rescue/rehoming can still be costly.) In anycase...just thinking out loud, I suppose...