I want to say Winamp 5 did not originally launch with backwards compatibility for old Winamp skins, but after enough people complained, future versions of Winamp 5 included backwards compatibility and the original classic Winamp skin. Being slightly larger made the player a bit too bulky for the types of docking you’d normally use Winamp for, and the alpha transparency and extended feature set made it significantly slower to render. Unfortunately a lot of people didn’t like it. It was based on the existing Winamp player layout, but the interface was slightly larger and it was given a more modern, “professional” look. To demonstrate the new Winamp skinning system, AOL had the Winamp team create a brand new default Winamp skin. Media Player had just added skinning support, and it went far beyond what you could do in Winamp – which is where you started getting all kinds of weirdly-shaped players, like the famous Windows Media Player Head. Winamp 5 launched with a revamped skinning system intended to compete with Windows Media Player.
AOL did what most big tech corporations do, and they messed with a good thing. Winamp was purchased by AOL (America Online, the internet ISP) at some point.
For most of my time using Winamp, I’ve mainly been using… well, this needs some setup, I guess.