The reason is that we don’t know Julian’s name. She was an anchoress, a religious vocation in which a woman was enclosed in a cell connected to a church, like a hermit, for life. Her vocation was to pray for the town (Norwich) and offer counsel to the people who came to her cell window. The anchor or anchoress took the name of the church, essentially giving up his/her individual identity as part of the vocation. This anchoress was at the church of St. Julian in Norwich. So while we know Julian definitely existed and wrote her spiritual work, we don’t know her name and precious little else about her. We only have her writing. No way could such a person be canonized today.
The teaching in the Revelations, based on her visions of Christ and Mary, is one of a piece with such teachings as the Sacred Heart, Spiritual Childhood, and Divine Mercy. It is enormously beautiful and consoling.