How can he monetize copyrighted content on YouTube?

I dont think so he is earning anything through this with monetization on. Now having said that, the other question is why does this guy keep producing more and more videos with copyright content & how come is not getting flagged?
I will answer the second question first. While publishing your video, you have an option in youtube to declare if the video contains copyright content. Declaring that safegaurds you from a ban but eventually you don't really earn anything.
Now coming to the first part, why is he every other week uploading copyright videos? That's a pure growth hack technique. If i were to today start a YouTube channel & produce my own content which is rich and engaging I might go bankrupt and still might not produce enough views and engagement. By using copyright videos what I am practically doing is
1. Gaining video views which in turn increases my channel views
2. Gaining organic subs
3. Creating High engagement
4. And finally preparing a base for my original video. With lets say a few 100k views and 10k+ subs on my channel, my original video will stand a much better chance of earning and ranking.

It isn't monetized by channel owner. Ads revenue goes to the owner of copyrighted material.

Channel owner can monetize with affiliate links in description but he can't monetize with adsense.

Maybe he gets paid while the content is not claimed.

I have seen people uploading WWE videos without even making an attempt to hide the WWE logo and monetizing it to make a lot of money. Just cannot understand Google's policies.

Prototype40 said:

why would you keep making those videos if you don't have any return?

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Some songs on his channel are covers without copyright.
The songs without copyright can be monetized.

SwiftDealer said:

With lets say a few 100k views and 10k+ subs on my channel, my original video will stand a much better chance of earning and ranking.

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Everyone here can choose in what they believe.
Some believe that there are super secret methods to grab instant cash.
Some already understand that in any case/platform, we should build strong base first, find audience, then monetize later.

Anirban Nag said:

I have seen people uploading WWE videos without even making an attempt to hide the WWE logo and monetizing it to make a lot of money. Just cannot understand Google's policies.

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And you know it is monetized by them? Look at this photo - this is what they see in their creator studio.

you can see music policies https://www.youtube.com/music_policies

The ad money doesnt go to him but to the owner of the material.

Anirban Nag said:

I have seen people uploading WWE videos without even making an attempt to hide the WWE logo and monetizing it to make a lot of money. Just cannot understand Google's policies.

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Yeah that's super dumb. Do your due dilligence, people