I had a thought about that... Maybe he just didn't belong at Starfleet Academy. I remember him saying, "I've done everything everyone has asked of me and more." When he got upset, that was his refrain. And that seems to be a hint that maybe he thought he was just supposed to join. Then Nick Locarno happened.
I always got the impression that he grew up in the shadow of his father, and he thought the only way to please his mother (who, moving from ship to ship, starbase to starbase, was the only constant in his life) was to sign up for Starfleet. But once he got out from under her thumb, he realized it wasn't his thing. Notice how upset Beverly gets when she finds out Wes is leaving the Academy.