Jupiter makes an orbit around the sun once every 12 years there likely are years where it is closer to earth than others.

Also there are years when it’s retrograde and there are years when it’s prograde so there is that too.

With Voyager it also wasn’t just Jupiter it was an alignment of all the planets which is far rarer.

And again voyager didn’t entered orbit it had a very brief flyby of Jupiter.

Cassini also took a decade to reach Saturn because it needed to enter orbit around it and its moons.