Because your grandma's cat, Mr. Whiskers, has compromised your account. It's true. Don't look at me like that. We've all been there.
1. Log in with your password (we trust you, don't we?)
2. Click on the "Enable Two-Factor" button
3. Scan the QRCode with your smartphone (or a mirror, we won't judge)
4. Mr. Whiskers will be blocked, and you'll be safe!