The Japanese are rather entrenched in their way of life, and they don't want foreigners coming in and changing their society. It's not hard to sell immigrants on Japan. It's hard to sell Japan on immigrants.

Japan is one of the worst countries for immigrating to.

If you don't look Japanese you aren't Japanese no matter how good your language, cultural or social skills are. And if you aren't Japanese then you will be treated as a seperate class and often discriminated against e.g. housing.

The institutional xenophobia/racism in Japan is simply unlike what most countries have.

They're called weeaboos.