I disagree with the implications, though the general premise is correct.
TL;DR - Music isn't getting worse, our definition of "Pop" has just changed to encompass shittier stuff.
There has always been crappy music. In years past, we just ignored it, or let it be a guilty pleasure. By some bizarre turn of events, that has flipped and pop music is entirely comprised of the shit and we're ignoring all the good stuff.
Take a look at the King of Pop, Michael Jackson, and the best selling album of all time EVER (by a huge margin) Thriller. The eponymous song was a genre defining EVENT in music history. It wasn't just a song, that was practically a feature length movie... but what chance would a 15 minute, 4th wall breaking music about dancing zombies and nerdy werewolf-ish kids (that don't look like Taylor Lautner) have in todays "Pop" music landscape.
None.
I'll also point out that the Music video started with 5 minutes of non-music, before getting to two full minutes of verse, another minute-thirty of Vincent Price speaking AND THEN a minute-thirty of instrumental before we get to the big hook ("CUZ THIS IS THRIIILER!!!") In total, there's just short of 10 minutes from start to hook. There isn't a single pop song today that lasts half that long in total, let alone start to hook. Hell, in 10 minutes of pop music, you'd probably be through 3 songs and a commercial or two. And EVERY SINGLE POP SONG will hit their catchy hook within 30 seconds of starting, guaranteed.
Again, the biggest pop song OF.ALL.TIME, released less than 20 years ago, wouldn't even sniff radio play today. Thriller didn't suddenly turn to shit
The other big problem is diversity. The study talks of homogeneity. These days, every Billboard topping single is pretty much the same genre, or really one of 2-3 genres. Once something is popular, studios race to produce 20 more artists just like them, and cash in on the craze. Back in the day that we had such talents as The Beatles, Elvis, Ray Charles, The Beach Boys, Stevie Wonder, The Stones, The Mamas & The Papas, The Supremes, The Doors, Marvin Gaye, Simon and Garfunkle, Hall and Oats, Smokey Robinson and the freaking Partridge Family putting out #1 singles. And that's JUST the 60s. You'll find similar lists of artists all over the creative map topping the charts in the 70s, 80s and some of the 90s. So yeah, you're certainly going to find less homogenization among the cadre I just listed when compared to the current generation's follow-the-leader slop.
All that said, we still have plenty of good music today, it's just no longer considered "Pop." Look up: Karnivool, Fair to Midland, Opeth, Ashes Divide, Coheed and Cambria or Hurt. Not saying you'll automatically like all of those, but it's a pretty good spread of styles, all very talented. Diverse, high quality music is out there ... you've just got to look a bit harder these days because it's buried under the mountains of generic homogeneous garbage that's churned out quickly and cheaply for the biggest profit.
Or you could just turn back the clock and listen to all the stuff from the "good old days." The old jams from Jimi, Zep, Clapton, Queen, Doobie Bros, etc haven't gone anywhere.