Classic Traveller had not yet been Niven-ized by some writers who though there had to be an excuse for people actually being on ships. That whole "AI sucks at jump" is a complete retcon created pretty recently. I had a thread about its origins a while back and no one could find any source in older editions. And even the Robot Handbook author only had a vague reference in the Deep Space Handbook or something for it. (Just to be clear, that Robot Handbook author was making a good faith effort to remain consistent with previous material, not adding fanon to the lore).
The original conception was that the computer calculated the jump using onboard software based on data provided by the ship's crew. If you did not have the software to do this yourself, you could get the plots calculated for you at the starport and just provide the final data once your intended insertion point was established.
That's why astrogators were optional on small ships. Your ship had to be more than 200 dtons before one was required. And, frankly, that was mainly for watch standing purposes more than that specific skillset being necessary. The space navigation skill was actually primarily about real space navigation in Classic Traveller.
Later, they phased out the Generate program and the jump tapes without replacing them with anything, like a lot of the early shipboard operations stuff (like engines getting damaged by unrefined fuel usage).
At some point, excuses were introduced as to why human navigators were necessary. Mongoose Traveller has now made astrogators a necesary role on all ships. And added a task check to the Astrogator's roll (that barely does anything) and all manner of modifiers to make it seem like its actually worth playing one. Including mechanics to make AI bad at it for mysterious Niven-esque reasons (since just being a person on the ship improves the AI's output without any astrogation skill being necessary).
However, at no point has it been made clear what was gained in gameplay terms by all this rigamarole. Or how it accords with the Charted Space conception of space travel being as routine as air travel, not something that gets f'ed up as often as any 2D probability would indicate.