I saw a case a while ago where the dog was being rehomed because he had chased a neighbour's cat that got into the garden, and the owner decided as a result of this she could no longer trust him around her children. Also recently dog ended up in rescue because he seemed a bit 'anxious and unsettled' when new baby was brought home from the hospital and they assumed this meant he was a danger to the baby, rather than just needing a bit of time to get used to a new family member in the house.
And there's also the one where family live in a small flat/house, have another baby and 'suddenly' realise they have no room (or time) for the dog any more. It's just outrageous, like asking for your older child to be taken into care because you've got no space now you have the new baby.
Of course there are genuine reasons dogs need to be rehomed, like Tally's case (what an awful situation and of course you did the right thing), or where the owner dies or becomes too ill or frail to look after the dog properly, or financial difficulties where people lose their house or get evicted and can't find dog-friendly accommodation to go to. But it would be nice if rescue places could be kept for these dogs, not needed by those whose owners just couldn't be bothered and see a dog as a disposable thing.