Code is not physical property

That's actually a relatively recent feature of copyrighting media. It didn't use to be that if you wrote a book you had an assumed copyright to it, you had to register for one.

This statement is somwhat inaccurate depending on how you scale 'recently'.
The Berne Convention established automatic copyright in 1886.
The US has been part of the convention since 1988. From 1790 to 1988 the US would've been under the Copyright Act of 1790, which did require registration, but that was over 20 years ago and not recent by the standards of most people, only recent in comparison to the ~200 preceeding years. More accurate to say 'for the majority of copyright history in the U.S.' than 'recent'.

And of course it's patently untrue for the people who've been in the Berne Convention since day 1 who've had 'assumed copyright' as a de facto standard for over a century and a quarter.