There's more to the polygamy issue than you make it seem. The practice of polygamy was never "OMG LOTS OF WOMEN FOR SEX", and in many cases it wasn't even about having more children. For example, by all accounts, though Joseph Smith had some dozen wives, the only one he ever slept with was his first wife, Emma. Other men were asked to marry and provide for widowed women who had lost their first husbands.
Also note that even among the early Mormons only a subset of men were asked to marry multiple women; it was not a general commandment for everyone. Furthermore, if polygamy is ever reinstated by the LDS Church as a practice here on earth, I do not believe the Church would mandate it, nor do I believe most Church members would practice it if given the option.
Among Mormons, marriage (when performed under the appropriate authority) is considered eternal. We do not use the phrase "until death do us part" in our marriage ceremonies. We believe it is better for a man to be married to multiple wives than for a woman to go for eternity without a husband.
I'll speculate on why God allowed it one way (polygamy) but not the other (polyandry), but before I do I want to make it absolutely clear that the remainder of this post is my own speculation and is in no way representative of official LDS doctrine.
One possibility is that more women than men are going to make it into heaven. In that case, assuming there is some benefit to being married in heaven, it would be better for some men to have multiple wives, so that all women can be married.
Another: it might be possible for married couples to have some manner of offspring in heaven. (Note that I am not referring to married couples becoming gods, I am merely speculating that since it is possible for married couples to have children during this life, perhaps it is possible in heaven as well.) If this is the case, then polygamy makes sense because a man can have children with multiple women at once, but polyandry does not because a woman can only bear the child of one man at a time; so, for the purposes of bearing children, polyandry offers no benefit over monogamy.
Again, this is my own speculation, and is not representative of LDS doctrine in any way.
At any rate, laugh if you wish. I believe God is omniscient, and I also believe that God has defined certain specific things regarding the practice of marriage. How can I argue with God? (That's rhetorical, please don't bother trying to convince me that I'm deceiving myself.) Experience has taught me on many occasions that God is much smarter than me, so I'm willing to trust Him on this.