Wrath of the Titans

Why can't they make a good movie based on the Greek mythology? As I recall Troy with Brad Pitt was the only one worth noting. The only thing Wrath of the Titans has is effects. They are really good. No credit for good characters in the plot ad they are all were created long long ago. They tried to merge several myths and obviously failed. Worst of all, the movie is totally meaningless. I don't get why they fight, for what and who are they. Why not just follow the myth then? They have a lot of sense.