MPA moves against lyrics sites

A story on BBC News reports that the MPA is starting to go after sites that post song lyrics.

So, if you have been trying to figure out what song that is that you keep hearing on your radio, better look soon or you will miss your opportunity to find it.

Can somebody explain to me again why it is in the best interests of the artists for customers who wish to buy songs not to be able to locate those songs using the lyrics? Or perhaps just explain to me why Apple's otherwise fine music service doesn't have that feature.