I think he does try for the finish. Watch the Hardy fight. It looked like he was trying to break Hardy's arm in the arm bar. And the Kos fight should have been stopped. They guy had a serious orbital lobe fracture as a result of being punched in the face for 5 straight rounds. The problem is that he is fighting the top guys in arguably the toughest weight class in the UFC. Easier said than done.
The submission attempt in the Hardy fight was in round one. GSP spent the next 4 rounds controlling Hardy on the ground. We all know that Hardy has a limited ground game and the fact that GSP did nothing but control Hardy is what I'm getting at. I feel that GSP could have done more on the ground to finish the fight, but that's not safe and comfortable for GSP.
Same with the Koscheck fight. Koscheck's eye was shut after round 1 and GSP spent the next 4 rounds coasting to victory in a safe manner.
I do agree though, even if he's coasting to easy victories and playing it safe, the fact that his skills are that much better than everyone else and allowing him these easy victories is remarkable.
There is no denying it, GSP is an amazing fighter, it's just frustrating to know that we aren't even seeing all his skills.