One big reason for launching when they did was the conjunction of the planets that let them slingshot past so many of them. Jupiter/Saturn conjunctions happen

One big reason for launching when they did was the conjunction of the planets that let them slingshot past so many of them. Jupiter/Saturn conjunctions happen every 20 years or so, but getting Uranus/Neptune in the mix (which Voyager 2 did, IIRC) is a lot more rare.