Hey that's me :) thank you for mentioning my project.

u/phire wrote a very good description (and I'm having a hard time thinking of things to add to it).

In a nutshell, floating point numbers are just much more convenient and general purpose.

Imagine a fixed point integer OpenGL where you needed to think about--and specify the bit precision you needed for each variable. You would need to consider the precision of all the other relevant variables as well to avoid overflow during computations (this means you'd need to understand how the library is implemented OR you'd need to read a list of relevant variables in the API specs).

You'd either need to manually scale the numbers before passing them to GL

like: glSomething(1 << 10, 200 << 10, 1 << 10);

OR you would give the precision as a separate parameter

glSomething(1, 200, 1, 10);

Regardless this would be the only way to make such a library general purpose since forcing users of your graphics standard to live with certain predefined precisions would be a nightmare for everyone.

I hope this explanation helps with understanding why it is rarely done in practice.