I think this is a design failure for this particular brake model.
Many of the mechanical brakes I've used have a sort of rounded "landing" surface for the cable, and the cable is rolled into it as the brake releases. When you apply the brakes, the cable sort of unrolls from it without flexing at the anchor point.
With normal use, the cable is flexed just a little bit and into a gentle curve, so no problem is caused.
On the brakes on your picture, however, it's apparent that the cable is flexed right at the anchor point. As you repeatedly apply the brakes, the cables are repeatedly flexing at this sharp point and the strands are broken by fatigue. (You can cut heavy gauge wire by sharply bending it back and forth)
Another observation is that with other type of cable anchoring, the cable always exits the adjusting barrel at the same angle, no matter to what degree the brakes are being applied, with the design on this type of brakes, the exit angle of the cable changes, and at some points it rubs against the inner part of the adjuster, which may also contribute to cable wear and may make feel the brake less smooth than it can be.
Here I show an example of a caliper that has this round part where the cable lands. Notice how the cable wont flex right at the bolt. (It may flex down where it leaves the receiver channel, but it won't be a sharp bend)
In my opinion, it is worth upgrading from these calipers. You may be able to find better mechanical ones, or even upgrade to hydraulic if budget allows.
I think there is nothing inherently wrong with good quality, well designed cable operated disk brakes. I used to ride Downhill on a bike equipped with mechanical disc brakes, despite all my peers "harassing" me into upgrading to hydraulic. I did never had a problem with the cable system, so I know good calipers exists. Hydraulic brakes are more expensive but can be virtually maintenance free (you'll only need to change brake pads when they wear out).
Do not skimp on brakes, as an accident derived from brake failure may end being way more costly.