You betray your own ignorance. Master has been used historically to refer to the "final" or "canonical" copy. For example, you make copies of a CD based on the master. Creating that master copy is called mastering.

The word "master" stems from Latin, meaning "great" or "teacher". Just as teachers pass on knowledge to students, data is copied from the master.

Any slavery related connotations is insanely recent, and arguably manufactured specifically for the purpose of linguistic censorship. Historically, slave owners were referred to as... owners.