Jedi are known as the guardians of peace and justice in the galaxy. Not soldiers, as Mace Windu pointed out. Becoming a solider takes away from your other studies.
From a meta standpoint, FFG set it up so that if you want to be outrageous with a lightsaber, your Force powers won't hit the same level. The Force is already a powerful asset that most characters don't have access to, so it prevents Jedi from becoming too powerful and unbalanced in the party... ...For instance, Influence can quickly put a Colonist face out of the job if someone sinks enough XP into it. If a Jedi character could become really good at Influence and lightsaber combat, then honestly, why do we have the Colonist? He's going to remain in the shadow of the Jedi who is better at persuasion and better at killing things. The only time the Colonist will get mileage is when the GM uses a species that is immune to mind tricks.
This present system lets everyone have their niche and while the Jedi are the most versatile (every career can get combat and non-combat, plus Force Powers to boot), they can't be good at everything.