Why does all new pop music sound the same?

I fall between the extremes here, for several reasons. First, I think "pop" music was always cotton candy to some degree (though there was material I liked and still pull out occasionally). The major labels were dragged into the "youth explosion" (say, post-Monterey Pop Festival) only because there was money there and a big market to be satisfied. A few savvy A & R people got it, but apart from The Beatles, which were kind of sui generis and acts that followed the British Invasion template -Sir Douglas Quintet anyone?- much of what was released in coming years followed trends. Psych- yeah, that lasted a couple years- not enough there to hold the mainstream (much as I love it). Prog- died pretty fast, wasn’t radio friendly, and the formalistic faux classical stuff just didn’t work for a lot of people (e.g., I dug ELP’s first album, but Pictures left me cold- I only revisited it in the last year or so, largely due to Greg Lake’s wonderful voice and acoustic playing).
The Band got some radio play, but were regarded at the time as under appreciated. (Their work didn’t really lead to a wholesale discovery of "roots/Americana" until the last few years). Disco and punk--some fun stuff, but kind of limited.
The ’80s had a sound all its own, much of it dated today. Then "grunge" with Nirvana, and a lot of follow on acts, some of which were pretty good.
Lurking on the sidelines, below the top 40, was the stuff people "discovered" for themselves, by word of mouth, through reviews, etc.
I think there’s good stuff out there today, but it may be harder than ever to sort through it-- very little money to promote coming from record companies and the splintering of so many different sub-genres that people follow through the Internet, much of it free. The flip side is that the Internet can give you access to a huge pool of talent if you are willing to do some digging.
Consider whether you were an adventurous listener at the age of 13-16, or whether you wound up listening to a lot of what your friends were into.
Some of the urban/hip-hop isn’t bad, though there are only a handful of those acts that I find musically interesting. Just like the ’80s sound, today’s "neo-soul" follows a template. Very little of it is innovative or engaging. But, I think the same could be said for almost any decade of popular music. You have to dig deeper to find joy.

FWIW, and this may be heresy, but I never really "got" Sgt. Pepper’s at the time of release and still don’t play it that often; when I do, it is a few discrete tracks rather than the whole album. Granted, it has been hyped as the best album ever made if you believe in such stuff, but my musical interests are diverse enough, as is my willingness to explore beyond the boundaries of convention, to find satisfaction in a variety of music, old and new.
+1 to @kennovak for throwing down some newer acts even if not all of them are appealing to me.

@chayro - that movie, of the three of them, was entertaining. I went with a guy who had at one point played with Link Wray. He was rolling in the aisle when "The Edge" claimed he invented the power chord. Pagey and Jack White are both OK in my book. 

@chayro - It’s a pretty good thread for other reasons too including musicology. The ’beat and hook’ formula fits with modern listening habits. We’ve all noted (I think) that music listening is background for other things, seldom an end to itself. So, having a beat (most of the modern pop I heard in the last few years was in the gym) and a hook every 8 seconds (instant gratification, hit the button again and again, filling up on empty calories) makes sense.
Musical taste is so subjective~ and it isn’t just age, background or culture. I trade listening notes, record tips, etc. with several people who are constant listeners and it’s like a Venn diagram- there are overlaps of varying degrees for each of us, but the bulk of what we "like" isn’t the same.
Does broadcast radio even have much significance any more with the ability to listen from a phone (whether plugged in, or blue-toothed, I guess, to a car, home system or on the go, with a playlist) or so-called Internet radio? (My wife had satellite radio in her car and I found it just as limited as heavy rotation top 20 type programming).
I actually dug Pandora for a while, mainly because of the "sound recording performance complement" model (driven by Section 114 of the U.S. Copyright Act). You’d plug in BB King and wind up hearing Skip James or Bukka White, introducing you to a range of similar but different performers and tracks. There were a few occasions back in the day where I’d hear something on the radio, hoping the jock would identify the track so I could go to Tower and buy the record. That part of the model still works in the Internet age-probably even better than before.