Cheat developers all want server code so they can analyze the cheat detection and sell more reliable hacks. Modders, pirates and preservation activists can skip a lot of complex RE work. Competing game studios might learn some new techniques. Abused workers want revenge. Script kiddies want clout.
It's a notoriously secretive industry with complex products, hostile work environments, lots of media exposure and heavy competition. There are way more incentives for a leak compared to some ordinary web app or business tool.
Claude Code could be another case where someone working at Anthropic decided to expose them. Or they did in on purpose because they wanted to show there is no secret sauce and Claude is really that good, but they were embarrassed to open source it and make themselves look like hypocrites.