Why does all new pop music sound the same?

Basically because it IS the same - I think anyone with ears already knows that, but there is more to it. 

@lowrider57 you mention a current hit factory...how is it different from Motown or Stax, etc.? I'm 38 and tend to think that I listen a wide range of music but I'm sure when my 2 1/2 year old is a teen, he may think I'm a musical schmuck as well. 

It's also important to note that not all music is made for you. Why would I sit here and spend time railing against a Taylor Swift album? It's not for me...I'm sure T Swift isn't sitting somewhere with her 6 string saying to herself "hmmm...I bet dudes pushing 40 will love this song..." I can say the same for Country music...something I will never ever understand but I can appreciate that many people do. 

You may not like what 'the kids' are listening to these days but It's important to understand what they are listening to because it's their soundtrack. I do not specifically care for trap music, Migos, Drake, Lil' Uzi Vert, etc. but this is what a lot of teens/20's are listening to at the gym. If I want a chance at identifying with them and staying somewhat relevant you have to understand what they are listening to and where it's coming from...

I hope I never become an old guy waxing nostalgia about Kurt Cobain (and the like) to anyone who will listen...my worst nightmare... 
Because in order to be popular these days it has to be generic enough to appeal to more diverse kinds of people in a vary basic way than ever. Much like fast food.

Better off forgetting about what is popular or promoted heavily and find your own good music. There is more of that out there than ever these days and growing. Its all up to you not others to find the music you like. The tools and material to do it is all out there. Some of it might even turn out to be or have been popular.

Don’t be afraid to go way back if needed. Great music was made and recorded as far back as the first 3rd of the 20th century and digital remastering and streaming works wonders. Way before The Beatles hit. Go figure!
I always thought the similarity to Pop music nowadays is because they share the same writers, and producers. If you have a producer who works with a pop starlet and they make tons of money then the record label will use that same producer for other pop stars till the world gets tired of the producer's schtick.
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.

Motown is a great example of a hit factory, and there have been others. I'm saying in the past there was more diversity on the Billboard charts. And I'm someone who was always seeking an alternative. 

I do agree that this is their time in music and pop culture, just as I had my day. But I'm not pining for it, I've moved on.

As the article stated, it's 1 or 2% making 80% of the pop music today.