The number 12 seems to be an important number in many spiritualities: Ancient Greek mythology, Norse Mythology, Buddhism, and Judaism just to name a few. Is the number of disciples just a coincidence, or did Jesus really have 12?
More can be said, but I wrote an answer to this a while ago: https://www.reddit.com/r/AskHistorians/comments/8lxmgb/do_scholars_agree_about_the_historicity_of_the/dzk0ebf?utm_source=reddit-android
Tl;dr: They probably weren't exactly 12 at all times and may not have been twelve specific individuals but some elements such as Jesus' prophesies and the presence of Judas in the narrative suggests he had a group of followers known as "the Twelve".