Why is my Apple ID locked

We are users like you, so we don't know why is was locked.

If this is in the iTunes/App Store, see the 3rd link.

See the Apple Support article(s) below. 

If your Apple ID is locked or disabled - Apple Support.   *

If you have changed your ID or password, have you followed the steps in this article? Make sure you turn of Find My Phone before signing out of the old ID. Once signed out and Find My Phone is off, then sign in with the new ID, then turn Find My Phone back on.

What to do after you change your Apple ID or password - Apple Support.     *

See the Apple Support article(s) below. 

If you see a message that says 'Your account has been disabled in the App Store and iTunes' - Apple Support.   *

Contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

Apple on Twitter