why would anybody sign in a browser game with their EMAIL
You can get the game on the play store if your more comfortable with that, but if your not on mobile then it's because there are saves in the game (like your name and stuff) and the chapters unlock in order (when u finish chapter one then chapter 2 unlocks and do on and so forth.) and creating an account can help save your data so you don't have to restart everything since it didn't save. Also it's so if you didn't remember your password to the account you can be emailed a code.