Games : Why does it seem like so few of the songs from the Minecraft soundtrack ever actually play?

I absolutely love the Minecraft soundtrack. However, it seems like that a very select few of the many songs that C418 has written and produced and released in the Minecraft - Volume A & B albums are ever actually played in the game.

Looking in the Minecraft/resources/music/ and Minecraft/resources/newmusic folders there are only a total of 14 songs (calm1.ogg, calm2.ogg, calm3.ogg, hal1.ogg, hal2.ogg, hal3.ogg, hal4.ogg, nuance1.ogg, nuance2.ogg, piano1.ogg, paino2.ogg, & piano3.ogg.)

Obviously, that explains the lack of variation in the soundtracks played, but does anyone know why so much more music was written and not used?

Edit:

Reading in the Minecraft Wiki (Volume B, Volume A), it appears that more music (from Volume B) is in fact included in the game, but is simply non-existent for me?