I believe the same is true with classical music, all that famous stuff is apparently copyright free.  I believe you can effectively create your own performances of those peices, and you would even own the copyright to your version, but not to the composition you had recreated.

In other words, you can't stop anyone else doing what you did yourself, and that's good, because you shouldn't be allowed to do so anyway.

it's not unlike the licence Blender is under I suppose (to an extent).  You can take it, you can change it, you can even sell it at a profit, but you can't stop others making use of and doing with your contribution, what you have done with theirs.  And this in itself brings up an interesting way to make money even from a free product, because if you look on Amazon you will find physical analogue books all about learning Blender.

They sell even at fairly high prices, and they get good reviews.
They sell because it's what people want, in effect, a high quality printed user guide.

Blender just grows and grows, so that means more and more opportunity to use a digital product (Blender) to sell a physical product (an analogue book), it's a perfect example, that is, another example of the analogue world being there for you when you've finally had enough of getting screwed-over by digital.

There are countless videos and tutorials for Blender on the web, likely more than for any other 3D program in existence.  It still doesn't stop people paying generous amounts of money for a physical book to learn from.  Because sitting down with a coffee and flicking through the pages of a printed book, is much nicer than surrendering to Adobe's PDF crap - so much so that people are prepared to pay for the priviledge.

They're selling their analogue books, releasing volume after volume after volume.  And when you're done with it, you can sell it on, give it to a charity, do whatever the hell you like with it - and that's exactly how it should be.