Because Twitch has a list of valid game names, as defined by the games endpoint:
League of LEARGENRDS is not in the list.
More generally, the HTTP error codes exist to be used, and ignoring them does developers a disservice. HTTP libraries have a bunch of features built around using the error codes. In my case, I’m going to have to put some extra logic in, that I wouldn’t have to otherwise, making my code that little bit uglier.