It might be a cultural-ideological reason that you think this way. Not every place in the world has those same assumptions and taboos. There are more blank slateist cultures where the only polite thing is to assume that any child can become anything. In other places people take it for granted that there are differences in abilities, talents, aptitudes, personalities that are fairly clear by age 10. In the US, this topic is too similar to how racists talk about blacks, so the whole thing is taboo. In places where the topic of innate talent does not have racial connotations (more homogeneous countries), people more readily accept it.

If you think modern Germany is homogeneous, well... :-)

If you think parent ever said then then we'll... :-)

It gets worse than that. Some of your life outcomes are determined by your genes and by your pre-ten-year-old lifestyle

Yeah, but we're talking about school systems here.

And with increasing understanding of epigenetics, even the lifestyle choices, and crises, of one’s grandparents could potentially influence life outcomes.

I wasn't surprised at all as a ten year old who got a recommendation for gymnasium and who didn't. It is a recommendation by the way, parents can chose to enter their kids in whatever they wish to. This leads to kids with high income / social economic status entering gymnasium and struggling mightily and kids from worker families who might make it not going to gymnasium.

It's not the rest of their life, just until they do it better. This is just the simple path. There are a dozen different paths in Germany's education-system.