just, why? P.S. there's no legal problems, sure you can have my words. and you can see Overwatch offering microtransactions to Japan with almost same system as D2.
Just adding my own two bits of speculation. I wonder if it’s because of the difference between PC and console. While consoles don’t have regional servers, PCs do. The Asia servers would likely also encompass China, hence the restriction. While you able to choose regions, I wonder if the regional game releases have the restriction. Just a thought.