I don't understand something.
The feminine form of Doctor is Doctress. It's not used anymore and spellcheck in my browser doesn't even recognize it. It's kind of sexist and implies that a female Doctor is somehow different from a male Doctor.
And yet, the feminine form of Mister is Mistress. It is still used, but is so over-sexualized that you don't find it as an option of official forms and such. It is, however, equivalent, as a Mistress is independent and can make her own mind up about anything and everything. She is neither dependent upon her father -- like a Miss -- nor her husband -- like a Mrs.
Why have we not moved toward a gender-neutral Mister? If it were gender-neutral, it would also meet the needs of the folks who would otherwise like a non-gendered title. (A group that is frequently subject to push-back and prejudice.)
Making it gender-neutral also bypasses all the old-farts who would refuse to add a new title to their official forms by using a title they already have.