Is there a reason iTunes doesn't have any songs by Tool?

I've looked for songs, albums, and nothing come up by them.
Itunes has to reach an agreement with the bands, or whoever owns the rights to their music. Some bands and performers have decided that they do not want their music on Itunes. Others like Kid Rock have signed exclusive deals with Rhapsody. You don't see any AC/Dc or Bob Seger on Itunes either, because they choose not to have their music on there.