Well, if we're going to flesh out the motivation of the Titans, we should probably understand what the Titans are in their conception. Lots of cultures have Titans, though some are not explicitly stated as such. Many are simply the Old Gods or the old ways. The way we usually understand them is by their contrast to the New Gods.
The Titans or Old Gods are Gods of much more primal forces. Unstoppable destructive powers from when man was in his infancy and at the mercy of the cruel and unforgiving world. Landslides, earthquakes, forest fires, floods, tsunamis, volcanoes, hurricanes, thunderstorms, freezing winters, famine and disease... These are the things man cannot fight, what wipe out whole villages in weeks, days, or even instants.
The New Gods are the civilizing elements created by man, representing all that they have built and governed to create and foster civilization. Gods of trade, war, wine, music, philosophy, language... These are the Gods of man's civilized world; what props it up and keeps it going. They beat back the darkness and the Titans and even in the face of great destruction can eventually rebuild and conquer the primordial forces of nature again.
This represents the ongoing struggle between the civilized order of Man and Nature, that which we build to protect and serve us, and that which we cannot control or even understand. An eternal struggle between civilization and the natural world which tear at each other in violence and subtle ways. Of course, there's sometimes the titanic clash at the end of days, when the Titans and the Gods of Man fight to the last and destroy each other, because Man must build on the Titan's world, and when he has destroyed the Titans finally, he has no world left on which to build.
Ideally, Man would come to respect the Titans, and live with them indefinitely, always wary and careful in his actions. But ultimately it is the arrogance of Man, reflected in his Gods, that will doom everything.