Liking someone's cat photo is the internet equivalent of letting their cat knead your thigh.
We've been posting photos and videos of cats on the internet ever since we got an internet. It's what cats were invented for. And it makes sense that people spend so much time soliciting positive feedback about their cats online, since they are definitely not getting any positive feedback from the cats themselves. The cat version of Facebook would have a "hiss" button, and we do not even want to contemplate which of the darkest corners of 4chan are already being run by our future cat overlords.