My friends and I created a roleplaying game. We don't like having many rules or having to find if a rule applies, so for an action a PC uses one of the following 9 statistics:

* **Strength**: For all kind of muscle actions (e.g. lift an object, push someone, hit with a hammer, hit with a slashing weapon (imprecisely)).
* **Dexterity**: Throwing, dodging, shooting, or movement related actions (e.g. jump from a tree branch to another).
* **Constitution**: Defines hit points and resistance to physical damage (e.g. a fireball to the chest is physical as your body burns).
* **Willpower**: Resistance to mental damages and ability to not become unconscious after suffering heavy damage.
* **Perception**: Basically using your senses.
* **Charisma**: Ability to convince someone.
* **Magic**: Ability to use spells of any kind.
* **Education**: Global knowledge. Useful against monsters, environment, or can be used to know the right people (e.g. "I know a mage that can do what we want").
* **Luck**: Could be anything. Used when any other statistic doesn't apply.

A player gets 450 points to distribute among his character's stats, minimum 0 and maximum 75. This is also the percentage chance of success of an action related to that stat: the player rolls a d% and a result under the stat score means success (e.g., a 75 in Dexterity means Dexterity actions have 75% chance of success).

As the GM, I decide the stat a PC uses for an action, depending on the kind of action the PC takes.

Problem
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The PCs overuse physical actions, and the PCs rarely take intellectual actions.

For example, a PC was jailed for abusing local villagers. The other PCs tried to break him out of jail instead of trying to convince the guard that the jailed PC was under the influence of some bandits' poison or whatever.

Breaking the PC out of jail means fighting with the guard, warrants being issued for the whole group, and possibly eventual banishment from the city to where convincing the guard it wasn't the jailed PC's fault could spring him no problem.

Some stats—like Charisma and Education—are only rarely used. 

This unbalances the game. Because the players' tendency is toward physical actions, they tend not to distribute points in the other stats (We've played many campaigns and many characters using this system, so the players kind of know what's coming).

I talked to them, and we all agree that all the stats have their place, and we can't just remove one or more, but I can't *make* them roll a Charisma action if they're trying to stab the guard!

We played one campaign where a PC had 75 Charisma and made full use of it, turning enemies so they'd fight alongside the PCs and taking control of a village by making the mayor believe the PC was a high-ranking soldier and that the PC needed the villagers. However, this is an exception, and, instead, they tend toward full offense, no brain required.

How can I "force" the players to use their PCs' intellectual stats more? Or is this a problem brought about by the system we've created and the statistics need changing?