BTW, guitar cables regularly handle signals that are only a TINY fraction of the strength of our line level keyboard outputs.
They need to be amplified MASSIVELY.
Any shielding problems, wiring inconsistencies and impedance irregularities are going to be massively amplified, too... Plus, of course, a guitar cord dangles out the back of a guitar and gets walked about, stepped on, jiggled, twisted around, just from the normal motions of playing the damn thing! (and don't get me started about showmanship pyrotechnics!).
Don't laugh at these things until you have walked a mile in THEIR shoes. Nobody is trying to sell an ARRANGER cable at those prices! Not even Ketron!