Why isn't Willpower important for Mages?

Summary: This is unfinished - currently collecting thoughts that might be contradictory.

Read an interesting bit of fiction yesterday: A Trinity of Primes - by Thaddeus Howze - Omniverse that led me to some thought while waking from an extended nap: Why isn't Willpower important for Mages in Generic European Medieval Fantasy RPG Nonsense (GEMFaRN)?

(I'm not sure which I'm more interested in: drawing out implications from published game mechanics or designing a system myself).

For this I'm not paying attention to later D&D Warlock are Sorcerers, which address this to an extent - I'm thinking mostly of original D&D (OD&D), Swords & Wizardy, Advanced D&D (1e and 2e) and similar games so my comments paint with a broad brush. NB: I use the term Mage to include "Magic-Users", "Wizards", and so on.

Intelligence

Typically, mages get benefits from higher intelligence: learning spells, the number of spells they can learn, the maximum number of spells they can learn, in some cases the number of spells they can cast in a day, and so on. They must refer to a personal spellbook each day to prepare their spells to lock their magical patterns in their mind for release within the next day. But there is no mechanical advantage to willpower, mental discipline, force of personality. Some of those things overlap into charisma and wisdom.

"Intelligence is quite similar to . . . intelligence quotient, but it also includes mnemonic ability, reasoning, and learning ability outside those measured by the written word . . . is the forte of magic users, for they must be perspicacious in order to understand magic and memorize spells . . . only the highest intelligence is able to comprehend the mighty magics contained in 9th level spells.". [1e PHB]

"It is absolutely essential to have high intelligence for a character who is a magic-users."

"Magic-users draw upon arcane powers in order to exercise their profession." 

" . . . [I]s usually assumed to possess a strange tome in which he or she has scribed the formulae for some of the spells known to the character." 

" . . . [Spells] . . . will have to have been prepared through study and research."

If magic is controlled through intelligence, then it is science. 

A 'science' that breaks conventional science or physics. I've long thought that magic in GEMFARN is temporarily breaking, or bending, the laws of motion, thermodynamics, conservation of energy and matter, and so on, by moving objects at rest, producing more force than the product of mass and acceleration, and similar changes to the math of the universe as we mostly understand it. (You could also say it's quantum-wuantum but I don't understand that enough to think or talk about it).

Some in fantasy literature (I'm not going to provide examples) describe mages shaping reality to their will. That's more along the lines I'm thinking, inspired by the writing linked above. The mage uses intelligence and knowledge to focus an energy that comes from either external sources or their own will.

If the sources are external, isn't that following a recipe? Mechanics? Scripting? Programming? 

In Mayer Alan Brenner's entertaining "The Dance of Gods" novel series, mages are effectively programmers applying patterns and routines to an energy source, which they collect or contain in a matrix. (I recommend these as light and fun novels and I don't want to spoil them on the off chance the reader might check them out).

GEMFARN, especially D&D, is generally silent about external power sources of arcane magic, i.e., wizard magic. But I think often implied by magic items and artifacts and some adventures. Magic places, ley lines, magic crystals - all those sorts of ideas. (What if the power source of wizard magic was taken from other universes?)

For divine magic, i.e., religious magic (clerics and druids), the external source is deities or nature (I would argue faith as a power source would also be internal, but one could argue that faith is sort of a measure of the bandwidth to the external source).

A somewhat dark thought is that in GEMFARN (or take the "European" and "Medieval" out of that for broader application) if people can be the power source for magic then that is a mechanical reason for blood sacrifices - increasing the power for a magic recipe beyond what an individual could. (And that's how you get giant ants, and spells of level 10 or higher). See also HackMaster 4E Blood Mage.

Wisdom

"Wisdom is a composite term for the character's enlightenment, judgment, wile, will power, and (to a certain extent) intuitiveness." (sic) [1e PHB].

" . . . [W]hile the intelligent character will know that smoking is harmful to him, he may well lack the wisdom to stop."

Extreme (19+) wisdom in 2e give immunity to various spells that overpower one's willpower or self-control: such as Cause Fear, Charm Person, Command, Friends, and Hypnotism.

The same idea applies a bit also to other classes

Clerics

Monks vs Martial Artists (Fighters)