This kind of crosschecking against all the works in the world is not necessary to do proper copyright checking.

Hold onto that thought…

there is easier algorithm for the same thing

That…isn’t easier. By a long shot. If anything, you made the “algorithm” more complicated by splitting works into different parts rather than look at the work as a whole. And not every work contains a notice of authorship; the first video uploaded to YouTube doesn’t display a copyright notice anywhere in the video, but it still remains copyrighted to the person who authored/uploaded it. You’re literally asking for employees/“volunteers” to put more thought (and work) into determining who holds a copyright on a given piece of media than the average person likely puts into whether their shit is copyrighted in the first place.

all you need to do is find all (C) notices contained inside the work

What happens when a work lacks a copyright notice — not because one was removed, but one was never put there in the first place? (Again, Night of the Living Dead fell into the public domain because of that oversight.) What happens when a work displays a copyright notice that names a corporate entity, but the corporation no longer exists and information about who actually owns the copyrights is non-existent (e.g., abandonware games)? What happens if a work is copyrighted to a company in a different country but licensed for distribution to an American company — who gets to enforce the copyright, and which company is in the right for doing so?

You keep thinking dealing with copyright is black-and-white simple. It isn’t. As has been told to you multiple times, the amount of creative works available to the world has exploded thanks to the Internet, and to truly check all copyrights — from the corporate-registered copyrights that “matter” to the Berne Convention–granted copyrights that every creative work has upon publication — you would need to check a given work against all others in existence. Not even Google has the resources to build a database that big, never mind check it with any expediency. And no such database could account for the principles of Fair Use, which means even the fairest and smallest of uses of preëxisting copyrighted content would get someone dinged.

And that doesn’t even begin to get into, say, false DMCA claims that are practically never pushed back upon in a court of law and other such tactics that route around “proper” copyright enforcement. Google has to treat those claims as legit until proven otherwise or else it loses safe harbor protections. Yes, that’s right: One of the most powerful companies in the world has little-to-no good reason to push back against even blatantly bullshit DMCA claims. (And I’m sure you think that’s a good thing.)

Sussing out who owns what copyrights where is not as simple as you’ve deluded yourself to believe. Google can’t figuratively snap its fingers and magically figure out who owns the copyright on a thirty-second cat video uploaded under a pseudonym ten years ago by someone who might have died in the interim between then and now. Your insane belief in the existence of a “simple” copyright system keeps you from even thinking about, much less addressing, the complexities of copyright that go beyond your simplistic black-and-white thinking. So long as you keep on thinking you’re in a world where copyright is as simple as High Card Wins, you’re never going to comprehend that it’s more like Texas Hold ’Em.

Keep espousing your beliefs about copyright. We here in these comments sections will keep debunking and dismantling all your failed, flawed, and frankly irresponsible beliefs about copyright — and copyright enforcement — with the targeted precision of a doctor with a scalpel. So please, I insist: Bring in your next patient.