Through conductive reasoning, I came up with certain "rules" that explain this.
This isn't 100% accurate, but here's how I came up with my ideas...
As for each profession, in the following charts the top row is the "rule" eliminating unusable weapons based on the used weapons in the third row. The fourth row shows other reasons why weapons that weren't eliminated by the "rule" are still unusable to that profession.
Highlighted weapons have unknown reasons for being unusable to that profession. It may have to do with aesthetics, or to limit the amount of skills (like what came first, the skill or the weapon?).
Because Necromancers and Guardians are opposites by theme, as well as Rangers and Engineers (nature vs. technology if you haven't guessed), they often don't share certain weapons.
Professions of the same armor category don't share certain weapons as well.
Also, when it comes to the weight of a weapon, the main-hand weapon has to be the same weight or heavier than the off-hand weapon.
Some rules are just made up, like how all off-hand weapons are light weapons.
This is purely speculative, but I find it to be a quite logical way of reasoning out unusable weapons for each profession.
Please feel free to let me know if you have any idea as to why a few of the professions do not use their highlighted weapons, or if you think the designers of the game didn't even think this hard into weapon choices.
To explain the highlighted weapons, I had the idea that each profession can only have two blade sets (greatsword, sword-sword, sword-dagger, and/or dagger-dagger); as for the thief's axe, I assume it's only because axes typically do slashing damage, while thief weapons usually do penetrating-type damage.
Edited by DaneVlll, 19 August 2012 - 05:48 AM.