Obi-Wan and Yoda were two of the most wanted men in the galaxy. All their brethren had been wiped out, evil was in charge of their government. They knew that Luke represented a chance for the Jedi to live again, for someone to defeat the Sith.
Obi-Wan went to Tatooine to give Luke to loving people and stayed (on a barren world he couldn't stand) to watch over and protect him for 19 years. He also used that time to commune with the Force and learn about maintaining his spirit after death.
Yoda, who took the brunt of the Jedi Order's failure on his shoulders, was reflecting on all that went wrong, trying to become more in tune with the will of Force (remember, they imply heavily that the Order had lost its way and become complacent and too attached to the whims of government). Though he had his doubts about Luke, he too was waiting for him to be ready.
Luke had a fleeting moment of weakness with Ben. One that pushed Ben off the brink and into darkness, costing him everything he'd built.
Luke blamed himself, and went sought out the long lost First Jedi Temple, so that he can... shut himself off from a galaxy falling further and further into war and despair (his naughty nephew leading the charge). He cut himself off from the Force completely, and stayed hidden so he could... eventually die.
The man who saw the tiniest glimmer of light in Darth Space-Hitler-For-Twenty-Years-And-Killed-Obi-Wan-and-Tortured-Han-And-Leia-And-Chopped-Off-Luke's-Hand Vader... immediately gave up without trying anything else, without using the knowledge in the First Temple to make himself a better Jedi and teacher, without trying to commune with the Force and learn more about the Dark Side within everybody...
I don't know, man. I'm seeing it again within the next week to see if it hits me better the second time but right now... I have a problem with that.