For the same reason naval battles in the real world weren't always fought by ramming ships into other ships. Ships are expensive, hyperdrives are expensive, and more valuable as ships than as ballistic mass. It would be a waste of resources for it to become a common tactic.
It was a lucky gamble that paid off.
>Maybe it's just that the original trilogy slipped in to me before I got old enough to where I think about such things
The OT is just as ridiculous. The trench run on the Death Star makes no sense outside of the context of the World War 2 film it was lifted from, no one in their right mind would design AT-ATs with such a high and vulnerable center of gravity, stormtrooper armor clearly does nothing against teddy bears and small rocks, spaceships bank and make noises in space, etc. Even lightsabers are just "cool laser swords" and metaphors for "space samurai" but don't make a lot of sense as weapons in a universe with telekinesis and blasters. Actual samurai weren't stupid enough to use their katanas if they had spears, bows and eventually guns available, yet I don't recall ever seeing a Jedi sniper, or the lightsaber version of a naginata.
Sound military tactics and plausible design were never really a thing in Star Wars.