The Dark One is imprisoned outside the pattern, and as an obviously powerful being, his biggest wish would be to escape. There isn't much to do against an obviously stacked Creator, and so he thinks that if he can break the wheel, then remake it, he can put a loophole or something there that will allow him to escape. This is childish in thought though, and like most children, a few things hold true. They enjoy destroying things, but don't grasp consequences. When they are told the consequences and put into time-out, it makes them sulky and something changes in them. They want to disobey, if they are harshly locked up in their room or sent to a corner. They also think that because they know the consequences, then they have control over them.

Children don't understand that certain actions are forbidden because they will not only hurt others, but will also hurt the children themselves.

The Creator, in the beginning, made everything. I don't necessarily believe it started like this, but alas, it's a theory, so here goes. It was a linear style universe, where the people went to a certain ‘heaven' and ‘hell' and stayed there for eternity. Then the Dark One, perhaps another ‘Creator' that had been spurned or shunned because he wasn't as powerful, jumped in and tried to rampage things. The Creator saw that if he continued, then his universe would soon be in the control of the Dark One. So he took the line and curved it into his wheel, where every soul was born repeatedly throughout the ages. In doing so, the Dark One found himself trapped within the pattern, unable to get away from what he had jumped into.
Now, the Dark One's permanent ‘time-out' may have been fought about for quite a while...a temper tantrum. That is why we have the times when supposedly the Dragon went to his side. They were times when he managed to cause enough problems that he ‘won'. But none of these held the key to making it linear or shattering it completely, and so he remained as he was. Trapped.
Now, the only way that he sees he might get out is to wait for the right age. I know this is far-reaching, but in the Age of Legends, no one even knew of the Dark One until they stumbled upon the ‘thinness in the pattern' and bored a hole into it. The Dark One, having gone through the cycles again, saw the pattern and ‘matured.' Now...the far-reaching stuff is that we have little mention of him trying to escape in the Age of Legends, or even to control Lews Therin. Of course there was the war, because this was an evil that the people had never seen before....but....they beat him quite easily, in my opinion, compared to everything that's continually going on now. He had seen what happened in all the other ages that he had tried to escape through and the difference now is that...he's found the correct age that will allow him to destroy and recreate, allowing him escape.

Because there are only ‘similarities' between ages, he has been unable to determine which age up until this point. I'm not sure how he figured that out, however, and therein lies my ineptitude on the entire matter, which might make this entire theory go to hell. But however he did discover it, this is the time that it all comes to a head. The Last Battle may not be the last, but it will allow the Dark One to escape and wreak his havoc on everything, all the other worlds as has been stated...and perhaps even the places outside of time. That would mean the destruction and downfall of the entire universe.

The Creator, of course, made the rules for everyone, and cannot even break them himself, but when he set the pattern into a circular motion, then he appointed souls that would be his ‘angels'. These are Heroes of the Horn, Ta'veren, and the Dragon Reborn. All play key roles when they are needed in order to lend something more than human, but less than creator. In effect, he is the gamemaster, and with a perfect understanding of the rules, sets it up so that if his creations also live by such rules, they can beat even the worst cheater, the Dark One. Now... there is also another point of interest I have fallen upon in devising this mischeif.

As a child does not realize that playing with fire will get him burned, the Dark One may not realize the full implications of what his actions may accomplish. He might become all-powerful and rule all in his darkness, with even the Creator under his heel...but the universe has been along the Wheel so many times that it does not remember how it can change into something else, such as linear. Now, this might be another thought onto why the Creator can't step in, but the main idea is this: Since the Wheel is such, then a sudden breaking might be like ripping the Wheel from the axle mid-trip, which means the entire wagon would most likely be crashing quite quickly. Even if the Dark One could pull off the Wheel mid-run and snap his own one back in place, it might not fit. Maybe his idea is actually a square or a traingle, and thus wouldn't work well enough with the other Wheels of the wagon to keep it working as smoothly as it should. It might not even fit the axle at all, and by that time, the original Wheel is gone and broken, with no replacement in sight.

Now, it's a lot to digest and wade through, but you've got this far, so let me summarize. The Dark One is in permanent ‘time-out' by trying to ‘color on the walls with crayon' where he shouldn't, and he was put there by the more powerful and mature Creator. The imprisonment only made him sullen, then so evil and vile that he would do anything to destroy the Creator's pride and joy, now in universally circular format. He thinks that if he can destroy the Wheel as it is by reaching into the pattern and jarring a few screws loose, then it will achieve what he wants, which I'm assuming is power over time and everything else in the universe. Now, if he managas to succeed in removing the current Wheel, it will either destroy everything, or, should his replacement be able to keep the universe working, give him what he wants. If there's anything else I need to go into detail on, please tell me, but that's what I've got for now. Have fun with it, I suppose.

Suravye ninto manshima taishite.

“Peace favor your sword.
- Alcair Dareis
“The Golden Spear”