Ranma and Weapons

A particularly common bit of fanon that really annoys me is Ranma refusing to use weapons. How did this become fanon? I understand why some things become fanon. There is generally some basis in the source or a spin off of the source (in Ranma that would be the manga with the anime and games being spin off). Other stuff is never really explained so some fan decided to come up with an explanation that would fit and others copied them. Those types of things becoming fanon makes sense to me, my real question is how do things that are countered in all forms of canon become fanon? I'd understand if Ranma only used weapons once or twice and it was missed by the fan fic writers but Ranma uses a variety of weapons quite often. There is only one time in the entire manga in which he makes any type of disparaging remark on them and in that instance it wasn't about weapons so much as it was the limits of combat. In the rhythmic gymnastics arc he wanted to be able to use his body as well as weapons (he didn't like the imposed limitation).

In the manga, Ranma has used a large assortment of weapons; some examples from the manga:
-Polearms. He had used a bo versus things in a haunted house, used saodake (literally bamboo pole but is term used for laundry poles which are now more commonly made from plastic), used brooms as weapons, cheer leading baton, tsuki nari yari (moon shaped spear), etc.
-Swords. He used a bokken (wooden sword) against Cologne and others during the Suikawari (watermelon splitting) race, the katana his mother carries around, sword during Pink and Link battle, etc.
-Whips. He used gymnastic ribbon, soba noodles, rope, his own hair, etc.
-Magical. Sentient fire breathing staff, shield that prevented poisons, magical joy buzzer type ring, ice staff he used in the battle versus Saffron, suggestion incense (multiple times), etc.
-Throwing weapons. Rocks, boulders, spoon, pencil, snack food (stopped Mariko's baton with a snack food), etc.
-Improvised weapons. Paper fan (to stop and redirect a punch from Happosai and another time to blow back incense at Happosai), spoons, pin wheels (used to pin duck form Mousse to the wall), tennis rackets (to hit thrown objects back at thrower), etc.
-Chemical. Sleeping power (on Kuno), Paralysis powder (On Shampoo), Chloroform (on Happosai), Alcohol (Happosai, Orachi), girl repellent (Happosai), smoke bombs (crowd of people to save Miss Hinako), etc.
-Defensive weapons. Shield versus Pink and Link, large boulders as shield, iron skillets (versus the Ashura), wears arm bracers, etc.
-Psychological. Bra's (versus Happosai), disguises (often versus half the cast), fake scary things (lizards, snakes, etc. on girls to scare them away from the girls dressing room), ax to scare cherry tree spirit, etc.
-miscellaneous that don't quite fit above types. Used mallets (On Taro, Ryoga, bean gun plant, etc.), blow dart to take out the principals balloon, bow and arrow (to send messages), Nunchucks, etc.

Even in the anime we see him training with Genma using a staff and he used weapons in corresponding arcs to the manga, like the rhythmic gymnastics battle. That is not a complete list of the times he used weapons and he has never showed reluctance to use them. So why did it become fanon that he doesn't use weapons?