I was taught that everything is created for a purpose, and perfection means fulfilling that purpose. For example an apple tree, is made to give fruit. If it is fruitful, has fulfilled it's mission, if not, it means that it hasn't reached the aim God had in mind for it.
Now, canonization means that the deceased person has fulfilled God's plan. A Sainted person cannot be called a barren tree, or a creature prevented from perfection for which it was created.
When you say that God created women for motherhood, either spiritual (nuns and virgins who pray and make sacrifes for others) or physical (matrons), you state that motherhood is the aim God had in mind (or at least one of the aims) for making women.
Why then did the church canonize so many girls who died in childhood? They were too young to be spiritual or physical mothers. Why did She canonize barren married women? and married women who had josephite marriages?
If these people ceased to fulfill the end of their creation, they could not be a glory for the Church.
Pregnancy is the means for creation of the child, not an end for creation of the mother. IMHO