"comments are not for extended discussion" is one of the biggest own goals of SO product development. Like, they had a feature that people were engaging with actively, and the discussions were adding value and additional context to posts, and they decided "yeah, let's kill this".

The people who run SO have some sort of control-freak complex. If there's anything I've learned from the SO saga, it is that oftentimes just letting a community do what it wants (within reasonable boundaries, of course) leads to a better and more successful product than actively trying to steer things in a certain direction.