Probably because most people want it to be both roleplaying and a game? There are story games for when you don't care about the mechanics at all.
Anyway, I don't get the impression that the OP had a problem with how often he rolled, but mostly with the baseline of how the mechanics reflect RP reality. He feels like a "good doctor" should have more mechanical heft that the +2 to +4 that is how they are typically represented. It has nothing to do with how often they are rolling.
NOLAtrav's point is well considered. Increasing the bonuses just means you end up increasing the task difficulty, so its numbers inflation without actually changing anything. That was also what I was getting at with the rolls being for dramatically interesting tasks. Can your Medic 2 ship's doctor do normal doctor stuff in a normal situation? Shouldn't even need a roll. In a high tension, drama filled situation? Then it's a roll. But if you aren't pushing up the character skills/stats to super high values, you don't need to push up the difficulty either. "This is an average dramatic scene of doctoring".
