> That notion only applies to patents and trademarks

You literally just gave an example above of that notion applying to copyright. There's no mere “seem like” at play here: the litigious music IP owners suing the pants off of musicians know full well that precisely zero musicians (least of all commercial ones) exist in a vacuum, and that's indeed the basis for the success of their litigiousness. Even if you can somehow prove you've never heard a particular song, You Live In A Society™ and that existing intellectual property's influence on society in turn influences subsequent creators.

There is, in other words, no such thing as true “independent creation”.

> Any court ruling that you would find beneficial for code copyright would mean that a human could have two windows open on their computer and cut and paste from one to the other and claim independent invention.

Don't threaten me with a good time :)