Update: ArenaNet has issued a statement confirming that it has disabled Guild Wars 2 gem purchases in Belgium.
"In order to conform to changes in Belgian law, purchases of gems, the Ultimate Edition, and the Ultimate Edition upgrade have been disabled for residents of Belgium," communications manager Gaile Gray wrote. "We are continuing to investigate more flexible solutions. We apologize for any inconvenience this may cause our players."
Guild Wars 2 may have become the latest game to fall victim to increased aggressiveness in gambling law enforcement, as players in Belgium can no longer access the game's Gem Store. As explained on the Guild Wars forums and Reddit, players began experience trouble purchasing gems last week, and Belgium is no longer listed as a billable location.
Belgium has been at the forefront of the call for more stringent regulation of loot boxes in videogames, which its Gambling Commission ruled earlier this year are against the country's regulations. The ruling led Valve to disable CS:GO loot cases in July, while Blizzard did the same to Overwatch and Heroes of the Storm in August.
The Guild Wars 2 Gem Store itself may not seem like a problem, but it facilitates "ecto gambling," an RNG-based form of in-game wagering, which Reddit user Altimos suggests could be at the root of the problem. The Gem Store isn't required for ecto gambling, but it does enable high-volume gambling for players willing to throw money at it.
"You can buy gems with real money, convert those gems into gold, then use that gold to ecto gamble until it's all gone/you've become rich," they wrote. "Either that or black lion chests."
Black Lion Chests are loot boxes that drop exclusive items, but since the issue seems to target the Gem Store as a whole and not the loot boxes themselves, it appears that ArenaNet is taking a more "big picture" approach to the problem.
ArenaNet hasn't yet said anything about what's going on, so it's all speculation at this point and I suppose it's possible that the store is just broken somehow—broken in an oddly specific way, in a part of the world that's recently taken a very dim view on the part of the game that isn't working. My expectation is that it's intentional, in other words, and ArenaNet has just done a really bad job of communicating what's going on.
I've reached out to the company for more information, and will update if and when I receive a reply. For now, if you're in Belgium and really want to buy some Guild Wars 2 gems, setting up a VPN should do the trick.