Why is modern pop music today so terrible?

Yes indeed Elvis did innovate the Rockabilly style. 

Passage of time doesn’t alter whether a musical piece is good or not .
What was an open mind at 20 would be an empty one at 80 .

I wallow in the past all day , every day , Bach is still perfection 400 years later ,

inna, there is a lot I don't understand , that's for sure .
One thing I do however is if I used your logic as a base 
 2+ 2 would equal 7 .

I thank God I knew a great songwriter who introduced me to J.S. Bach when I was twenty-four. For the "richest", deepest music, I turn to him, with increasing frequency and consistently as I have gotten older. One has to listen to him last in the day, as he is a hard act to follow!

I imagine if he were alive today, JSB would be deep into EDM.