I was thinking of using epoxy at first for holding it, but it's too pricey for me, and you can't do maintenance with it once epoxied. Also, most cable makers I know just use heat-shrink tubing instead.
It's something you can buy in bulk in DIY shops; I think they have different sizes. I mainly see them used for 8 cores, but even then most people would just use heat-shrink tubing lol.
That's what I thought at first too, but after seeing so many cables and "reverse engineering" them, it's much simpler than I thought; they're easier to solder than earbud drivers. The hardest part for me was braiding them lol.