after I reset my MAC it is stiil saying your account is locked

Reinstalling your OS does not alter your Apple ID or it's status with regard to your Apple ID being locked. All the installation does is replace the OS on your local computer. What's happening with your Apple ID is not touched.

How did it become locked?

What you reset is not clear to me.

The following may be relevant though: If you see an 'Unable to sign you in to your Apple ID' message - Apple Support.