Why does yahoo deactivate your account?

I am a little angry as I went through all this hard time of creating a profile for my personals and now its gone due to them deactivating my account. I had no idea i had not checked my email in that long but why do they need to wipe out everything without a grace period? This is hard work trying to create what you had and also losing all your emails and messages from the personals and the email account. its not fair!!!!