Well, there can be many answers to this. It is one of those questions where one can only guess. In the early works of Beckett, there is a certain kind of misogyny and one also finds a curious gender-absolute in much of Beckett's works. In plays like 'Waiting for Godot' he gives us the impression that there can be no other gender in the world apart from the male while in his late-plays like 'Rockaby' & 'Footfalls', the very idea of there being a single male figure in the human world is out of question. The absence of women in 'Waiting for Godot' has been popularly related to the play's cynicism in cancelling out a possibility of redemption through the reproductive cycle of life. The absence of a female, I think is also due to the fact that the relational scheme of this play is homosocial if not homoerotic. Didi and Gogo are a 'pseudocouple', to use Beckett's own expression. In a radical Gay figuration of the world, where does the woman fit in? Another way of answering the question would be to see Godot as a woman/mother. In this sense, the play might be seen to represent the invisibility (patriarchal) and unknowability (psycho-analytical) and yet the irresistible desire to know the feminine enigma. if truth were a woman, can Godot not be a mother? Vladimir and Estragon are like two kids who look forward to an impossible encounter with the Other as love.