Major websites like YouTube gather logistics on every little thing that can possibly be clicked on or otherwise interacted with by their users. This information drives direction in design, and in the case of YT it's about the only thing. The problem with this principle being their only one, or by far their most influential, is that it inevitably leads to designing in such a way as to cater to teenagers and people in their 40's and older. Why? Because the former is by far their largest demographic(s), and both groups tend to lack the Internet savvy to understand certain sorts of things on a site, in order to navigate it better, use its other various functions / options, etc. Ultimately those of us who have standards, loathe restrictive and watered-down web function and appreciate good aesthetics end up getting shat on. So if enough people neglect to roll back their channel page layout, regardless of their reasons, the monkeys at YT will be commanded by their overlords to continue working on the newest layout, and might end up nixing the option to roll back for future programming conveniences or whatever else. I doubt even a single person who had spent time working on their page sometime in the past, to make it look nice / neat or what have you, was pleased with this new look.
I had a good look at what the new style had to offer - then reverted to the old one, simply because its better. Progress is one thing, but bad, unnecessery progress is far worse than none at all. .