Other females writers from the time who used pseudonym such as Jane Austin (Mrs Ashton Dennis) and the Bronte Sisters (Currer (Charlotte), Ellis (Emily) and Acton (Anne) Bell) are now published under their real names yet we still call Mary Ann Evans by her male pseudonym. Why is this?
She did not only use 'George Elliot' as her pen name, she used it in her everyday life.
Note that 'George' can be a short form of female names such as 'Georgina' or 'Georgette' it is a unisex, rather than a male name.
She continued to use her George Elliot pen name after it was public knowledge that 'Mary Ann Evans' was the real authoress behind her work.
It may be worth x-posting to /r/AskLiteraryStudies