well,,,here's my guess.
ok. melkor tormented elves and hence came the orcs. and Treebeard says that, in the same way, trolls were made in mockery of the ents. i believe that in the time right before the Last Alliance, Sauron wished to possess as much land as possible for his strength to build. So it is possible that he wished to possess the land in which the entwives dwealt. And i think that Sauron captured the entwives and created his own race of trolls, the olog-hai. Then the question would arise: Are then all the trolls female? Well,,,would anyone really be able to tell the difference between a male or female troll. And the same with orcs. Anyways that what i think happened.