User reports: https://steamcommunity.com/discussions/forum/0/4362376335340911703/?ctp=2

Likely because Steam has not complied with local laws (in fact, they have no local presence at all on Vietnam).

I do wonder if Steam is going to do anything. Complying with Vietnam's regulation is probably too burdensome to be worth the revenue, but on the other hand, Steam's promise with their DRM has always been that they would "unlock" the games if they had to shut down, and now they're shut down in a specific country.

Vietnamese Steam users have been sold products which they cannot play at all anymore, at least while following the laws of their Communist (so, totalitarian) regime. It's not a great situation for them.

Well, to be honest, they're probably going to do nothing. But I do wonder to what extent Valve, who knew they were not in compliance, should have not sold games at all in Vietnam? Similar to the Helldivers situation, surely they knew this shoe was dropping.