Robertson wanted to be paid for his good design. Henry Ford didn’t want to pay, even if it was a tiny amount.

Ford was willing to use an inferior screw design that could cause production issues rather than pay a license to use the superior design. And, even though the patent expired a long time ago, these decisions have momentum.

I would bet that Torx is more popular than Robertson even though it’s a much newer design. Is it a better design? To me, Robertson seems to have the edge when it comes to simplicity, but Torx could be better for industrial applications because multiple lobes that have a surface perpendicular to the direction of torque probably gives it more control. Also, thanks to Ikea, I’d bet that hex-head bolts are incredibly common. They share most of the benefits of Robertson. I suspect they’re a little less efficient though because the closer you are to a circle shape, the less the faces of the screwdriver tip align with the direction of torque. I wonder if there are advantages of hex over square, since you see hex so much more often.