Why does all new pop music sound the same?

The generation gap argument is valid, but music was never packaged the way it is now. Look at the artists who top the Billboard charts and tell me they are not part of a manufacturing process by the same hit factories.

I only surfed past Dick Clark's Rockin Eve, but I heard enough to know that this contemporary genre of music sounds like it was written and produced by the same group of music manipulators.
Of course, using certain "hooks" and style has happened before over the years; e.g., disco, but never so tightly controlled and accepted.

There are a few exceptions in this genre like Lady Gaga...I give her props because she writes her own songs and has been formally trained since a very young age.

But there's plenty of good off-mainstream stuff to hear if you do your homework

This is true, but we always had to search to find alternative music.

And yet the high school seniors I teach have a musical knowledge base and listen to a wider variety of artists than my generation ever did at that age. 

@simao , the college interns and recent grads I work with in the film and video field generally do not know or care about the history of modern music. Some listen to Pop/Rock, many listen to recent alternative bands (some that I know, most I don’t), but have never heard of the bands that influenced the music they like. For instance, I’ll hear music coming from a work station and I’ll comment that it sounds like Smashing Pumpkins or another alternative group (1980s, 90s), and they’ve never heard of them.

I don’t expect them to know Led Zeppelin’s music, but weren’t they exposed to their parents’ music while growing up? I knew about Perry Como, etc. as a kid. That was my what my parents listened to, I listened to Top 40 or Rock.

The iPod generation has missed out on an incredible music education.

I've been a musical outcast most of my life. Never really took to mainstream music much with the exception of the truly (IMO) talented like Bowie, Dylan, Steely Dan, etc., who were somehow able to put non brainless music on the radio. That stated, there is so much excellent music available to us today. Literally decades of it.  

I respect the opinions and I realize the validity of those who say we think all new music sounds the same because we are "OLD", as if that is a condition, which it probably is. But, anyone with actual ears knows that Zeppelin did not sound like SLY, did not sound like Joplin, did not sound like the Who, did not sound like the Fudge, did not sound like Creedence,  did not sound like Earth Wind and Fire, did not sound like Blood Sweat and Tears, did not sound like Jethro Tull, did not sound like the Stones, et al. Whether our parents thought it did or not is not relevant because our parents were musical schmucks for the most part. I’m addressing a group of people who pretend to actually know and like music. Contrast this to most of today’s popular music, which is predominately written by the same two people, using the same formulaic hooks. Yes, there are probably many newer artists with validity, but they will never get the airplay or make the money of a Taylor Swift, Chainsmokers or whomever, who could not kiss the musical ass of anyone mentioned above. IMO of course.