Why is modern pop music today so terrible?

I'll go with one explanation that hasn't been proffered yet - changing taste in recreational drugs.

Back in the day, downers and hallucinogens sparked a more pensive or spacey (respectively) artistic impulse.  Today's turbo charged uppers produce 200 bpm EDM.  It's especially tough on us old guys who can't listen that fast.

I thought we're talking about popular music. 
Popular music has it's own agenda to be popular and targeted to uninformed crowd at all times. Any idea why Leonard Bernstein was NOT part of Boston Pops? I guess because music isn't really part of radio pop and it's definitely a separate meaning.
Tchaikovsky back in his days published piano pieces 12 Months in 12 journals so that casual and barely trained person could entertain oneself with relatively easy sheet music.
Today there's no need to know sheet music, because it could be heard on radio and radio is guilty of all charges to deliver popular music. I had music basics as a school curriculum to know basics of SolFegio, therefore I guess I value complexity and effort to play certain piece or perform. 
Did anyone enjoys David Rose or Ray Conif? That stuff will trigger my "wtf am I listening to..." phrase. It's pop.  

Can't stand most music that sells millions of copies ( or downloads or whatever) in any genre these days.  Can't stand the Grammy's or CMA Awards either.  But I couldn't stand "Yummy, yummy, yummy, I've got love in my tummy" or "Bang Shang a Lang" when I was younger, either.

Bad music is always around.  Even allowing for vast differences in tastes, it is puzzling why really terrible stuff is so popular.  Maybe consumers just don't seek out better music or don't seek to refine their sensibilities.  I don't know.

But there have never been more good musicians as today.  In the past couple months, I have seen Lyle Lovett's Large Band, Frank Solivan and Dirty Kitchen, Branford Marsalis Quartet with Curt Elling,  Mark O'Connor and the O'Connor Family Band, The Brubeck Brothers, one day of the Rockygrass Bluegrass Festival, and Chris Eldridge and Julian Lage.  Monstrously good musicians, all.

Let others crowd stadiums to hear the flavor of the month.  I don't want to hang out with them anyway.  I will look for, and easily find, plenty of music that utterly knocks my socks off, recorded, broadcast and live.

Support live music, folks.

Styles change but there’s always an abundance of talent. Mahler once observed that "the younger generation is always right" after hearing a piece of Schoenberg’s (that he didn’t even like). Ed Sheeran, John Mayer and Jack Johnson, for instance, are tremendously talented. Do I buy their stuff? No, but there’s no doubt that the gift is there. Had they been born decades earlier (or had I been born decades later) I’m sure I’d have liked their music. And as someone pointed out, there’s always some stuff that seems ghastly. I heard a half hour of some really lame, unimaginative music courtesy of the local classical station this afternoon. Arnold Bax, Michael Torque (sp?)--really dreadful IMO. I would have preferred any of the 3 pop stars I mentioned earlier, actually.

"Pop" became a derogatory term in the late 60's, particularly amongst my counter-culture hippie contemporaries. I didn't let that stop me from listening to the "shiny", studio-produced sounds I still preferred to the overly-long (imo), extended solo blues-based ramblings of Cream, Hendrix, Led Zeppelin, The Dead, etc. In the late 70's and 80's, my Punk and New Wave-listening contemporaries were bewildered by my love of ABBA and The Rubinoos. Their loss! Though looked down upon by my Country purist friends and associates, I even liked Shania Twain. Steve Earle called her "Nashville's highest paid lap dancer". A guilty pleasure, for sure!