> Also the former national railway company decided to not build new crossings at all.

At least partially that's actually the law as well – the default mode for new rail-road crossings is mandated to be grade-separation, with exceptions to that rule decided on a case-by-case basis, though primarily only in cases of low traffic (which in case of roads means ≤ 100 vehicles/day). Plus in actual practice the federal railway authority also having a reputation for a strict interpretation of that paragraph and tending to not grant exceptions has also done its thing, so in practice new level crossing on the federally-operated railway network (i.e. DB) are indeed a total rarity.