The problem is that the MP3 format is so ubiquitous. It's so easy to just provide an MP3 when someone needs a compressed format. FLAC (and Ogg Vorbis, APE, etc) may be superior but there's still an element of uncertainty with respect to codecs, player compatibility etc. Especially in commercial players, car stereos, etc. MP3's just work. Suck but work. LOL.