There's an explanation for all that. Lucas has said Obi-Wan was originally intended to play Qui-Gon's role, but be torn over whether to train Anakin. He eventually decided to split him into two characters, the believer and the skeptic.
Therein lies the problem, I've always felt.
I always thought Ben Kenobi shouldered a great burden for tutoring (and therefore being responsible for) a villain of galactic proportions, and his years in exile were penance for his errors. I always felt Old Ben had a wonderful melancholy about him, a lonely old man who was once great and respected, living away his remaining years in exile because of his one great mistake...
Afte the PT, Obi-Wan is kind of absolved of all responsibility. He trains Anakin because of a promise he made to his dying mentor, NOT because he actually believes in Anakin. When Anakin goes sour, Obi-Wan can even side with Mace and Yoda and all the other Jedi who felt Anakin was trouble, saying 'I told you so's' to Qui-Gon's ashes. Qui-Gon Jinn, long dead, is the sole architect of all the woe that befalls the Old Republic.
I feel that there would have been more poignancy if Obi-Wan had been the sole supporter of Anakin, and there, in the end, Anakin's fall to the Dark Side would have been a fabulous betrayal of Obi-wan's sole trust.
Also, I always thought that having two Jedi in PHANTOM MENACE was stucturally unsound. Qui-Gon has most of the narrative spotlight, and Obi-Wan, whom we all want to see more of because he's one of the only OT characters who shows up in Ep1, has nothing to do (narratively) until the Duel of the Fates.
If Obi-Wan had been the one making all the decisions (going to Tatooine, taking a chance on Anakin in the PodRace, trusting to the Force in light of more logical choices), then suddenly every bad thing Anakin does when he goes bad becomes Obi-Wan's fault.
What do we care if Qui-Gon's to blame for trusting Anakin? He's dead by film's end and has absolutely no narrative weight in the OT. If Obi-Wan's the Jedi making bad decisions, then there's a thread that runs through the WHOLE 6 films. Not only is Obi-Wan an important character in the PT, but in the OT, his training of Luke can be seen as his last attempt to correct a decades-old mistake that has had dire consequences for the galaxy.
Which is kinda how I thought of Kenobi all these years since EMPIRE, to be honest!
-Adam