Supply and demand, capitalism 101 pure and simple.
If enough well educated, well trained, well experienced, well qualified 'Asians' (Japanese usually get higher offer) refused to work for a quarter of salary of a comparable Europeans then in theory the companies will have to offer more to attract them.

Unfortunately, in practice for every Asian that refuse to work for a quarter of the European's salary there are ten more lining up to work for one-fifth.

I think the question should be re-phrased: Why would company hire a European/American/Australian/Japanese etc for four times the salary of a comparably qualified 'Asians'?????

Cheers
SK