9 months is a typical direct transfer, using a traditional rocket engine whose thrust is so high you can basically treat it as infinite: accelerate up to your transfer speed in a few minutes and coast until you need to slow down in a similarly negligible amount of time. You need to set a lot of gas on fire in those few minutes, though. Electric propulsion is so low thrust that it can't put you on that kind of direct trajectory in one go, so the trip is more of a slow spiral around the sun with continuous thrust the whole way. The tradeoff for everything taking forever is unbelievable fuel savings, which is a surprisingly common occurrence in space travel.