It's rather foolish to say that Asian countries are ignored by customs in any country. Every country has its own set of tariffs, according to their own economic & political reasons.
The reason a country like China has such a huge trade surplus with the rest of the world is that we in the West have given them preferential trade agreements. By allowing Chinese products to come into our countries cheaply, we have hoped the Chinese would reciprocate & allow us access to their vast domestic market.
That this hasn't actually happened is a political matter.
As for the rest, it all comes down to the basic laws of supply & demand. Over the past years,
Tamiya have faced huge competition from new rival manufacturers; Vallejo,
Revell, Lifecolor, Mr Hobby to name but a few. Add that to increasing shipping costs & the supply goes down, along with the demand and prices inevitably go up.
The rise of nontoxic acrylic paints have really pushed the use of lacquer thinners into the wilderness - hence why buying
Tamiya Lacquer thinners is nigh on impossible these days.
Secondly, shipping by air has become prohibitively expensive in the last 10 years. So everything comes by sea. The minimum amount of cargo on a ship is one cubic metre. That's 1,000,000 cubic centimetres! Imagine how many 10ml pots of
Tamiya paint you can fit into that space
So when we order directly from Japan or another Asian country, it takes a while because the exporter has to have enough orders to fill a full cubic metre.