When the new customization page on Tumblr was introduced, there was an uproar of complaints from users everywhere. Fact of the matter is, the Tumblr population isn't very fond of change. Changes made to the customize page; changes made to the Terms and Guidelines — change isn't always good in our eyes.
The complaints about the new customization page died down, namely because the classic customize page was still up and running. We were given the option to use the customize page we were most comfortable with. Then, out of the blue, the classic customize page vanished. Tumblr users no longer had the option to choose the customize page they preferred; the one they were more comfortable with.
All we ask of you, Karp and Co, is to keep the classic customize page up and running. I think it's safe to say that the classic customize page is not only simpler, but easier to understand.