It appears that Jesus attracted a band of followers which included both men and women. There appears to have been an inner circle which included Peter, James, and John, who have the most written about them, and who accompanied Jesus in the Transfiguration story.
The other apostles have bit parts, and their names vary across the Gospels. Several of them get no mention in the Gospel of John.
Also prominently mentioned are Mary Magdalene, Martha, and Mary, mother of Jesus among the followers. Aside from the resurrection stories, Mary Magdalene, Joanna (the wife of Herod’s steward!), and Susanna are mentioned in Luke as following him and providing financial resources. (See Luke 8:1-3)
So why twelve? Twelve is highly symbolic of the original 12 tribes of Israel. There were 12 sons of Jacob (renamed Israel after wrestling with God). So there had to be 12. And they were sons, so they had to be men. This was highly symbolic that the project of Jesus was tied in with the history of the Jewish people. So I look at “the twelve” as a literary device used in the Gospels to show God’s providence in a literary way.
A more interesting question is “why were the women mentioned at all in a culture that gave women no standing?”
All the accounts of the empty tomb originate with the women, who were the least reliable witnesses of the day. They could not even testify in court. To me this countercultural fact indicates that the women were involved in a big way. Perhaps the men had fled to Galilee to save their own skins. But in any event, the women were so prominent in the resurrection story that authors writing several decades later had no choice but to include them.