I doubt law is a problem here. Champions and Star Trek lack different servers, for example, and it seems like I can buy Zen through the website just fine for them. I suspect it's either an oversight from Cryptic (most likely) or probably a misguided attempt to avoid people buying stuff for the "wrong" server and…
Steam allows purchasing Zen on Dragon without the need to use a VPN. But yeah, regional restrictions are super dumb. Why do they even exist if both Dragon and Drider are run by the same company?
I am a relatively new player with little stuff of value. :) Also I am playing a WW2 shooter that recently disabled DX9. However, so many people complained that they reversed the engine update afterwards. So there is hope Cryptic will see reason too.