Why is modern pop music today so terrible?

Exactly. Pop music is terrible in all time periods, just probably getting worse and worse. And that's good - let's see how bad bad can be.

One note: pop music by definition is viewed differently depending on perspective.  
If you were 13 in 1962, the Beatles was the most amazing band ever.
If you were 19, the Stones was WAY cooler, much more the street band and avant garde of the time.  The Beatles all cheesy pop music!  Plus they can barely play their instruments. 
If you were 35 in 1962, you may well have thought the Beatles absolutely sucked, 3 chord garbage.  Give me the big band that was at least comprised of musicians who could play.

Brad

In 1962 if you were in America you probably had not heard or heard of the Beatles at all.

Also, the Beatles played their own guitars all the time, except for Clapton's solo on the White Album.  And they played their instruments every bit as well as the Stones.  Eventually, far better.  The Stones were for people who thought they had to be a little bit cooler, less mainstream.  Both great bands, BTW.

czarivey: great list of bands!  A friend off mine recorded the EWF album that is without doubt iconic.  It was an extremely controversial "sound" at the time, very clean and clear, no distortion or lack of dynamics. Not at all the Motown/Stax sound and he was NOT hired to do the subsequent albums.  Yet, that record (September, groove tonight, etc) still sounds contemporary and current.  This is a GREAT example of sound of pop changing over time with great moments.
Brad