This works well with games like hearthstone because the game itself is well defined. Whereas sandboxes such as Minecraft, Roblox and MMOs such as Runescape, World of Warcraft would be greatly neutered by this restriction. An an example of this, the Minecraft community is currently up in arms about Microsoft's new chat reporting.

There's also an entire category of games games (2nd life) and non games (omegle) which are built on communication with strangers. For some people that's part of why they play these games.