The fact that any cabeling is a lowpass filter is worse than the propagation delay, so if the signals are high frequency (witch they are, a dmd uses dithering to make grayscale, so a lot more than 60fps/1080p)
if your cabeling has too much capacity/inductance than your signal gets distorted enough to be not working.
Thats the matched impedance thing, the traces on the pcb have a fixed distance to each other and to the ground plane underneath. To "control" the signal distortion.
You can do this in cabeling harness to, but its really complicated. First you need to know the wave impedance thats used on the PCB/DMD, your cabeling needs to be exactly the same to reduce reflections.
That requires very specific conductors and isolation and distance of the conductors, not easy.
You need a special cable with the exact same length on all pairs, if you make your own, thats difficult to do. I have tryed to make longer labels for LVDS Display long time ago, and it was very difficult, the length must be matched very closely, and see the above section about impedance matching.
You need the exact same length because the image data gets splitted between different pairs to reduce the frequency needed to transmit the data.
if one pair is longer than the others the data arrives late at the dmd, then the dmd can not identify what the data meant to be.