Those restrictions are made through use of trademarks, limiting access to development tools through contracts and code signing.
First can be sidestepped by not mentioning the trademarks of the platform holder anywhere.
The second can be side stepped through reverse engineering.
Third can eventually be hacked out of the device (like the recent encryption key reveal on Intel CPU's) and was not applicable to older generations.
Proof of 1 and 2 is the existence of new games developed for ancient consoles.
https://www.syfy.com/syfywire/the-unlikely-but-very-real-res...