If it’s this easy, why don’t people just do it? And why haven’t I heard of this before in all these topics?
Because people don't know about it.
Also, for many people, even doing something like "sending an email to counter claim" is too much work for them to bother doing it.
You'd be surprised how many people won't follow through on something when there is even the smallest barrier to them doing so.
> And why haven’t I heard of this before in all these topics?
Things can get to be pretty technical, when people are talking about the minutia of a counter claim to DMCA. It does not surprise me that info like this is not well known.
It is provided on the official copyright.gov website.
All this stuff is in a searchable database that is helpful provided by the US government, and is required by law.
Ex for Google:
https://dmca.copyright.gov/osp/publish/history.html?search=G...
But it's more likely that you get a Youtube takedown, which is not related to DMCA. There's a UI for that in the mgmt. console.