The WALL nuts are terrible. Came with my Houdini power supply upgrade. The wire came out of the WALL nut, which is very easy to do, the wires don't sit very well in there. I got the WAGO nuts and LOVE THEM. reusable, so much better than a wire nut. I bought an assortment set and found tons of uses for them already.
The reason they would NOT be used by pin manufacturers is cost IMHO they are ALOT more money then a molex connector or soldering.