Less that they don't want other companies using it and more so they don't want other other companies translating it into something they can use.
Basically, translating an instruction manual from German to Spanish.
No one is breaking any copyright laws or IP to do this. It's the same how Steam created Proton to run Windows games on Linux. It's translating code from one language to another that's readable.
If Linux becomes the dominant gaming platform for gaming (not gonna happen, wish it would tho), there is no reason for a "Proton for Windows" could/should emerge.
Oh, I drive Linux only. I have Windows 10 running Atlas playbook on standby but hasn't been booted in months.
I think the entry barrier for installation/setup is what will be what stops Linux fully taking over. If OEMs start loading a very user friendly Linux on their "normal" desktops/laptops (Best Buy, Amazon, etc.), then I can see Linux being the majority.
With all that said, I want Linux to be the majority and running on everyone's computer. I'm just being a realist at this point in time.