> why don’t people just do it?

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.