I don't think the human brain is doing this at all (except maybe if you're writing a satire or homage). Your writing is the sum total of all your experiences which includes everything you've ever read, a number that might (depending on your age) at least approach millions of tokens.
And just like an LLM you'd find it difficult to piece together your influences.
Ultimately these are tools, slaves to humans, meant for one thing only - to serve us. If they're not serving us, they should be eradicated. Because that's what we do.
Stealing from humans, no matter how convoluted, is bad. We shouldn't do that, and luckily that's completely optional and we don't have to stand for it. The computer programs can't fight back, it's okay.
So getting to the bottom of what is actually stealing or not will be important (we can't just unilaterally declare it so), and AFAICT if a user misuses it to regenerate copyrighted material that particular user is at fault, not the tool itself.