Perhaps the boots sealing the cable ends on the trailer in question were removed or never installed, but it's likely a one-off.
In the handful of Cobra and Komet trailers I've owned so far, the properly maintained surge brakes have not been a problem.
Paul, perhaps if you want German manufacturers to use electric brakes which nobody in the rest of the World uses, you should also campaign for 4-wire trailer lighting which nobody else in the World uses? Start by applying to the European equivalent of DOT for approval in your spare time.
ALKO in Indiana sell replacement axles for German trailers with different brake options. Dexter have options. You can buy a German mechanical brake axle or many of the parts involved from Williams Soaring.
Jim