According to Mormons, why did God make Eve's childbearing painful? This question is about the following explanation from this page at lds.org:


  “If Adam had not transgressed he would not have fallen, but he would
  have remained in the garden of Eden. And all things which were created
  must have remained in the same state in which they were after they
  were created; and they must have remained forever, and had no end.
  
  “And [Adam and Eve] would have had no children; wherefore they
  would have remained in a state of innocence, having no joy, for they
  knew no misery; doing no good, for they knew no sin.


And the passage in Genesis 3:16 (NIV) records the following statement from God to Eve after the "fall":


  To the woman he said, “I will make your pains in childbearing very
  severe;with painful labor you will give birth to children. Your desire
  will be for your husband, and he will rule over you.”


The question is: why would God make Eve's childbearing severe and painful after the fall, if the fall was needed for them to accomplish God's plan?

(I would have thought the verbal expression from God in this case should then have been something along the lines of "Yesss! Congrats! You chose well, both of you. Now go forth and multiply.")
While there may not be a direct answer, that is specifically answered in LDS (Mormons) doctrine, there are a few that together may provide an answer. The LDS have a strong belief in opposites.

2 Nephi 2:11


  For it must needs be, that there is an opposition in all things. If not so, my firstborn in the wilderness, righteousness could not be brought to pass, neither wickedness, neither holiness nor misery, neither good nor bad. Wherefore, all things must needs be a compound in one; wherefore, if it should be one body it must needs remain as dead, having no life neither death, nor corruption nor incorruption, happiness nor misery, neither sense nor insensibility.


The LDS also believe in having children and that they are a blessing. Elder Neil L. Anderson said:


  It is a crowning privilege of a husband and wife who are able to bear children to provide mortal bodies for these spirit children of God. We believe in families, and we believe in children.1


The LDS understand that pain is part of being mortal2.

But like everything pain has it's opposite: joy, happiness, etc (which come later). (in my words)

On intense pain Elder Robert D. Hales said:


  In the past two years, I have waited upon the Lord for mortal lessons to be taught me through periods of physical pain, mental anguish, and pondering. I learned that constant, intense pain is a great consecrating purifier that humbles us and draws us closer to God’s Spirit.3


See also:

The Family - A Proclamation to the World

Opposition in All Things



1 https://www.lds.org/general-conference/2011/10/children?lang=eng

2 https://www.lds.org/general-conference/2005/10/the-sanctity-of-the-body?lang=eng

3 https://www.lds.org/general-conference/1998/10/healing-soul-and-body?lang=eng

Emphasis added by me