Netflix's Enola Holmes introduced viewers to some whole new members of Sherlock's family — but why did Sherlock abandon his mother and sister? Intelligence clearly runs in the Holmes family tree. Sherlock Holmes proudly considers himself the world's greatest consulting detective, his brother Mycroft is indispensable to the British government, and in the world of Enola Holmes his little sister is a veritable genius as well.
And yet, as intelligent as all these members of the Holmes family may be, they don't really get on all that well. Even the relationship between Sherlock and Mycroft can get pretty strained on occasion, and in Enola Holmes it is clear Sherlock hasn't visited his mother Eudoria and his sister for years. This difficult family relationship neatly explains why Enola isn't mentioned in any of the classic Sherlock Holmes stories. But just why did the Holmes family fall apart so badly?
A definitive answer is given in Nancy Springer's Enola Holmes books. These reveal the family fell apart after the death of Sherlock's father; his mother then actually banished Sherlock and Mycroft. Eudoria was unhappy with the misogyny in Victorian society, and she would have been fully aware neither Sherlock nor Mycroft had any intention of changing that culture. What's more, she fully intended to bring Enola up as a potential world-changer as well, and her sons would have rather gotten in the way.
In the Netflix film, Enola asked Sherlock why he never wrote to her. Sherlock told her he was simply too busy, and there was probably truth in that response; he's something of a misanthrope, with only a limited knowledge and understanding of social norms, and so he probably forgot about his family while he was focusing in on his various detective cases. But he was also likely of the view that correspondence would not be welcome, simply because he had left his family home under such unpleasant circumstances.
Clearly Sherlock was wrong. Though he did not know it, his little sister pored over the newspapers looking for any mention of her big brother, and she collected clippings of his adventures. It's clear Enola loved her big brother, and deeply desired a relationship with her; her near-worship for her mother blinded her to the fact Eudoria had turned Sherlock away, though. Fortunately, now Enola Holmes has headed into London to set herself up as a detective for herself, she should have plenty of time to spend with Sherlock.