They think you might be a criminal, literally. Discord has a big problem with people conducting illegal activities on their service (buying, selling, and providing support for cheats, black hat hacker communities, harassment and stalking, etc. The list is pretty long)
Something about your account + connection makes you look very similar to people they know to have done these things. And discord decided that the risk of having these things on their platform is a greater threat to their business than the risk of people like you quitting the platform.
They do this so that if regulators, law enforcement, or one of their business partners comes to them with evidence that you're using discord to do bad shit, they can help track down the real person behind the account.