Truthfully? I get why he did what he did too, except for the 'not looking for Dean' thing. I think he might've made at least a cursory attempt but when it became clear that his resources were extremely limited and there were simply no clues to be had, only then would he have considered retiring.

All that being said, there is SO much about Sam's behavior that is shrouded in mystery and I'm sure things will come to light that'll clarify the reasons for his choices. Show always manages to pleasantly surprise me!