It's easy enough to explain. Rock derives originally from the blues, and one of the classic blues riffs is called the '12-bar' blues - it's 4 bars of the root chord, 2 bars of the major 4, 2 bars back at the root, 1 bar of the major 5, 1 of the major 4, and then 2 more at the root. You can hear it in the old (Adam West) Batman theme really well.
Many of those 'learn to play guitar' books start out with teaching the 12 bar. Throw in riffs and bridges, and you have a pretty decent foundation for music that can fit words, just like learning how to write a sonnet or a limerick.