Yeesh. Prohibited? Then how do you decide who gets a promotion? At random?
Many German companies are not, in fact, unionized, and tend to pay 'übertariflich / außertariflich' - instead of union protection, they just pay you significantly more than you'd get with an union job. Which is a good thing 9 out of 10 times.
Which - incidentally - is why such companies advertise paying 'außertariflich' in their job adverts.
Situation might be different for low- and non-skilled workers.
The answer probably isn't American work ethics inspired by American compensation schemes, but rather Chinese ingenuity and grit. But seriously, why can you build so much on 35 hours per week and a mid-five-figure salary?