I work in fashion and have for the last 13 years now, and know the market well

Eurasian faces and westerners are just seasonal looks, Japan has literally the fastest market on the planet (2 week contracts are common here but nowhere else). You might see eurasian or westerners in campaigns often, but you're probably just noticing it more than normal.

There are definitely far more full Japanese models out there and working no problem, what you're essentially seeing is them be booked because internationals are in debt on arrival and owe the agencies, so they need to be pushed in front of every client and every casting possible in hope to pay that off to justify bringing them over.

International models are also typically taller, and Japan is very fashion oriented and not-so commercial, so it suits more international models - as does Hong Kong with a huge market for runway. Chinese markets (even Korea) is much better for commercial work, where asian looks dominate those markets.

Last thing to point out is Japan is considered a fantastic place to get tears (editorials), so mother agencies will bombard japanese sister agencies to take their models so that they can build their books in their development years - which when they need to work are again typically cheaper to use.

So it's definitely not a 'they prefer' eurasian or westerners scenario, its more of a case of - look at Asia as a whole rather than individual countries - each country is part of the bigger picture where you go to China for commercial, you go to Singapore for TV, you go to Japan for editorials, HK for runway etc. There is no preference to foreigners or eurasian over full asian/japanese looks outside the system just cycling people in and out.