I think it's just because of availability. I can't find this one at any larger component store when I search for it.
However, if designers of split keyboards would instead mirror and panelise their designs then having a symmetric connector wouldn't be an issue. A panelised PCB design might even be cheaper to produce if the halves have a weird shape that could interlock inside a rectangle.
BTW. The TRRS connector had been chosen because it is compact, which was important for a case of layered acrylic when you want to use as few layers as possible. It is common for it to glitch, and you get noise if you turn it.
If split keyboard cases instead were made with tenting, there would be more vertical space under the raised side of each PCB for a more reliable connector: mini-DIN, 4p4c or even one of those aviation sockets that seem to be so popular right now...