LDraw.org allows third party part in the LDraw Parts Library

[Matt Chambers]

From my perspective the reason is because S-Brick is explicitly made to be used as a supplement for LEGO as opposed to Cobi which is a clone brick brand competing against LEGO. I’m sure you could find some sort of counter argument but at the end of the day it’s on the judgment of Chris Dee, the Library Admin.

Doesn't S-Brick compete against LEGO's remote control solutions?  How do Cobi's studs-on-top-and-bottom bricks compete against LEGO, which has no such bricks?

Perhaps the distinction is that S-Brick competes against LEGO in a very limited way whereas Cobi competes in a quite broad way (they produce many of the same brick shapes, only a few exclusive ones). But I'm only suggesting for (currently) exclusive bricks to be added (it would be silly to duplicate parts for each clone brand when they are meant to be interchangeable).