
I can see how rescues get out of hand quickly, all rescues are overwhelmed, and they're usually ran by dog lovers who can't say no. I don't know anything about this particular one, but they seem to have had a lot of dogs that you shouldn't really rehome, that look like they could fall under the XL ban. I can imagine they were flooded with desperate people wanting rid of their dogs and then it all just became too much. I'm not excusing any of it at all, but I do understand how it could happen.
I help out with another rescue and as well as the kennels overflowing the person who runs it often has 12 - 20 dogs in cages in their house, and still desperate pleas come in, dogs going to be PTS if they can't take them. If the owner were to be ill for a week or so it could all get out of hand very quickly.
Personally I think there are worse things than death, if a dog is likely to be waiting years, or possibly never rehomed then it should be put to sleep.