Why would anyone give up a young dog to a rescue when supply and demand means they can sell it for hundreds of pounds or even more?
Because the supply FAR outstrips the demand.
This is like the housing boom - people paid far too much fr property as prices spiralled. They all thought that brisk and mortar never one down in value - they were wrong. One day, all of a sudden, the bottom dropped out of that market and thousands were left in negative equity with properties they couldn't afford to sell, or to live in.
This will happening - probably is happening - with puppies.
Paid £5,000 for a dog.
Get sick of it - try to sell, but no-one will pay £5000 for a half grown pup when they can get a cute li'l baby for the same price.
SO the dog is reduced in price until someone wants it, or it is dumped.
Or someone buys it and breeds from it, so the whole circle starts again. And it is bred from and bred from until its health is destroyed, then it is dumped.
Or they get sick of it, and it is sold on. And again. And again.
And every time it is sold it becomes more and more anxious, and less and less "lovable", and more and more difficult to control because it's frightened and doesn't know what's happening to it.
These stories rarely have a happy ending, unfortunately.