Why do humans keep woofies when we know they're useless?

It's the hierarchy of usefulness; people have an innate need to feel superior, and since they have no possibility of feeling superior to us, they had to look elsewhere. It's way to easy to feel superior to fish and hamsters, just because of their size, plus neither or those will play fetch with them nor with they stick their cold wet noses in people crotches, and for whatever reason people really like that.

So they started playing with dogs, and the dogs, knowing a good thing when they see it, decided to dumb things down a little bit so that the people would give them bones loaded with meat (because that's what they did in the old days, like the 60s and 70s), and they happily played all the stupid games people wanted them to.

So now people keep dogs around because they think the dogs are lower creatures here to serve them, when the truth is the dogs are smart enough to play the game. So in a way, dogs aren't useless...they make our people feel good, and when the people feel good, we get treats. And it's all about the treats.

Then again, thinking about it, you might have been asking about useless humans...which is a whole other answer...