mis'aveh l'tefilasan shel tzadikim

The gemara (Yevamos) tells us that the Imahos were barran because Hashem desired to hear their prayers. Surely, as the meforshim ask (see Tiferes Shlomo, hashlamos to vol 1) and as anyone who has children will tell you, having children is not the end of one's efforts in prayer, but rather is the start of a lifetime of prayer on behalf of the needs of those children. Why would Hashem have not given the Imahos children in order to inspire those prayers? And more importantly, are we not c"v suggesting that G-d engages in sadistic sport by making the righteous needlessly suffer just so he can hear their prayers? My wife has a nice approach which she wrote up here - take a look.