Jupiters sphere of influence is full of radiation, meaning the sat needs a lot of shielding which makes it very heavy. Additionally, you need a lot of thrust to not only get to Jupiter, but to be able to get into a geosync orbit around a planet other than earth, so youre gonna need a lot of fuel. And finally, time... Europa Clipper just left earth, it will be 8 years before it arrives at jupiter. The windows for launch are long but very spread out, so mission timing would be important too.
And, funfacts time.. Clipper is going to europa but will be spending much of its time in orbit around jupiter, passing closely to europa every orbit. This was done to limit the amount of radiation the sat will get during its mission, and that orbit is uuuge, in order to avoid as much of the radiation as possible.
The area of Jupiter and its moons is probably one of the most hostile space environments in our system, catching asteroids, radiation, huge planet full of gasses that would corrode you and your ship if you dipped in, and a huge gravity well that makes it difficult to leave again once youre there. Not many other planets in our system are as dangerous as jupiter and friends.
The SLS option would have entailed a direct trajectory to Jupiter taking less than three years. ... The move to Falcon Heavy saved an estimated US$2 billion in launch costs alone. NASA was not sure an SLS would be available for the mission since the Artemis program would use SLS rockets extensively, and the SLS's use of solid rocket boosters (SRBs) generates more vibrations in the payload than a launcher that does not use SRBs.
On the opposite end of the spectrum, New Horizons was only 478 kg [1] and still holds the record for the fastest thing ever launched from Earth. It also did a gravity assist flyby around Jupiter and it still took 9 years to get to Pluto.
To expand on this a bit, it's the fastest launch. The unqualified speed record goes to the Parker Solar Probe in 2018, and was previous held by Helios B way back in 1976.
The distinction here is that New Horizons has spent it's life traveling away from the Sun, and it costs energy and thus speed to do so. Meanwhile, solar probes gain speed during their fall towards the Sun.