Also, Google has to maintain a forest of separate identities for everyone. (youtube, gmail, g+, etc). It's super annoying just to maintain one login. There's huge business value in consolidating those, even without adding features.
Finally, Youtube comments are a cesspool. Even when they're not racist or threatening, they're immature and, at best "wow that's awesome". They drive viewers away. I bet google wants to try to do-over comments in a way that makes them useful to people, not unsettling.
And I would hesitate to call it a disaster. Sure there's a lot of whining about it now, especially in tech circles, but every big interface change comes with a wave of whiners. We'll see in three or four weeks if anyone is complaining.
They'd certainly have a much tougher time doing this if there were another option for the masses, but for most people YouTube is it. Saying people are going to quit watching or uploading to youtube is silly, they'll go where? Vimeo?
They're going to keep tweaking it, people are going to adapt and learn, videos of cats falling off objects will continue to be uploaded.
ps: "How do they keep morale up"? Free food and big piles of money. How else do you do it?