> Japanese government weren't so xenophobic

Japanese people are, this is normal.

They look at what happens to people that aren't xenophobic and they don't want that.

Not all cultures are trigger happy with irreversible population replacement dynamics, and simply don't consider mass immigration as a viable option. This is completely normal too.

Unfortunately peoples lives are very short to see things play out in the long term, and in the long term cultures that are okay with population replacement dynamics are very likely anomalies.