There IS a biological difference, but it's compounded by the social factors for sure.
If there are even VERY SMALL difference on average scores on whatever attribute, you will tend to see those differences magnified at the tail ends if the ability is statistically a normal distribution
Taking a gender-neutral example: If Gender A has an average score of 110 on something, and Gender B has an average score of 107 on something, then it is very likely that the top percentiles of this particular trait will be overwhelmingly represented by Gender A.
Biologically, in most real normally distributed traits, men tend to have a "flatter bell curve", meaning there is more variance in whatever trait it is, and women tend to be statistically more clustered towards the mean. This means that men are typically over-represented in both extreme tails (far below average as well as far above average). See "variability hypothesis" https://en.wikipedia.org/wiki/Variability_hypothesis
And on top of that, you need to find people who are also highly motivated and disciplined (conscientiousness, one of the biggest differences between men and women in terms of personality traits) AND are interested in things, not people (primarily men, one of the biggest differences between men and women in terms of personality traits), AND are in the top percentiles of the traits associated with being good at eSports (e.g. visual-spatial awareness, reaction time, problem solving, hand-eye coordination, micro-motoric skills and more). To find people who are high on most or all of them continues to lower the prevalence of women the more circles you add to the "venn-diagram" of necessary traits.
Let me caveat very clearly: I am not saying that women cannot be good at esports, and I'm not saying that it is impossible for women to be better than men
It is the classic "chess problem". The odds of finding women that are high in all traits necessary to be a top esports player are simply significantly lower than for men.