Part of their identity is shockingly low TFR (Total Fertility Rate).

In Japan, it's 1.26 live births/woman. In Singapore, it's an astounding 1.04. Both are worse than Europe (1.46) and the US (1.66).

That’s super unfortunate and I’m well aware, but it’s a separate issue.

I don't see how it can be separated from the culture as a whole. After all, what causes such differences, if not differences in cultures?

Since this inverse correlation with birth rates and GDP is observed everywhere in the world, I'm certain we're not speaking of a cultural issue.

It's not a terribly good correlation; there's a lot of variance that could well be cultural. Unless you think it's explained by genetics?