To be honest, while I used and loved Winamp for a long time and it would be nice to have the sources even for a 2.x version, the reason it was popular back in the day was because it was the only one (or close enough). Nowadays there's a million ways to play audio files. Audacious even has a mode that imitates the Winamp aesthetics, and I think it can even load Winamp skins. There's not much value in the Winamp sources beyond nostalgia, and if it's about that you can still run ancient builds on modern Windows, although they're not able to play anything.
I think the moment to release the sources was when Nullsoft went down. Back then Winamp still had a smidgen of mindshare left. Now everyone has moved on to either streaming or other players.