Adoption on Windows was definitely an issue for that time frame. Even as someone that was willing to adopt strange software, or compile it on Windows, it just wasn't worth it for the cross-platform use (mostly for mobile devices at the time, including generic players, and iPods).
I started using RockBox around 2005/2006, but it still wasn't worth converting my entire music collection to Ogg Vorbis from MP3. Right around that time, my vehicle stereo could suddenly support MP3/WMA files, and I could burn multiple albums to a CD for my truck stereo. MP3 had the broadest support across devices, and basically become an industry standard, even with the licensing.