People don’t seem to understand the difference between stealing and copying.
When you copy something from someone, you have a copied object and the other party has the original object, or maybe vice-versa.
When you steal something from someone, you have the stolen object, and the other party no longer has what you stole.
This is why stealing an idea is so fundamentally different and difficult. Proof of possession requires you to take that idea, and manifest it into the world to the point that there is no doubt that that idea is yours and yours alone.
A task made more Sisyphean, because furthermore all ideas exists in context and as derivatives of ideas past and present, local and global. To carelessly claim ownership of an idea is like asking for a deed to a wave in the ocean.