Weapons and armor are technological developments, no different from computers and software.  Like computers and software, they tend to get developed based on an "arms race" sort of mentality.  A new CPU comes out for the public?  There will be games developed capable of slowing down the new powerhouse to an unplayable crawl, creating a demand for a better CPU, etc. etc.  The development of weapons and armor was the same.  If no one had developed axes and falchions capable of chopping through leather and brigandine easily, there would have been no need to develop cut-resistant chain.  Fully articulated plate, and later fluted plate, was a response to crossbow bolts and the like; the arbalestier (crossbowman) itself was an improvement on the longbow archer, and would have replaced longbowmen entirely by the 15th century had the mechnaisms of the crossbow not been so expensive to manufacture.

In addition, the lack of effective communications technology prior to the 19th century meant that technological developments tended to stay regional.  The mastery of swordmaking in feudal Japan stayed right where it was, while the rest of the world putted along with their low-grade broadswords or, if they were lucky, a weapon manufactured by the master smiths of Toledo.  The Turkish-Mongol composite bow was never adopted into European technology, despite the fact that Subedei had destroyed about 80,000 Polish, Hungarian, and other troops, considered to be the best in the area, with a 20,000 man diversionary force armed with these bows, in a matter of days.  Neither does one see exotic weapons like the whip sword, patar, bagh nakh, han-kyu, etc., in the world of dark ages combat… that is, until fantasy gaming.

What does this mean for the the world of fantasy gaming?  In a typical swords and sorcery sort of milieu, weapons tables are filled to the brim with weapons of every possible description and era, and from cultures which may or not have been appropriate.  There are completely ridiculous inclusions, such as the availability of rejected weapons like the fauchard and the lucern hammer in a world that had developed the halberd.  Also included are weapons which may look cool and bizarre, but have absolutely no place on the battlefield, like the bagh nakh, kryss, etc.  Armor should technically be available based on the armor-defeating potential of weapons available at the time, yet we find a mixture of every possible form of personal protection, regardless of the fact that the "high end" weapons on the weapons tables are capable of defeating most armor types with ease.  There are exceptions, like buff coats for archers who are expected to die anyway in close combat, and maille and brigandine taken from the corpses of soldiers unfortunate enough to be wearing it when they were mercilessly killed, but a "trip to the armor store" should yield little more than the highest level of affordable personal protection available in that time and place, with a few lower end items for the cost-conscious killer.  There is simply no demand for anything else amongst the "elite" social class of "adventurers."  (This becomes apparent in games like D&D, where by second level all fighter types have bought plate mail.)

However, somebody put them in there, and so instead of repairing the damage, a designer will "tweak" weapons with arbitrary and ridiculous values for damage, speed, etc.  This leads to more inaccurate game interpretations of weapons, as one game relies primarily on the absurd tables and stats of its predecessors as source material.  Designers and developers, having implemented stupid ideas like "feathered Aztec armor" and "really little knife" in a world of articulated plate and estocs, want to give players a reason for wanting to use these inferior armor types, hence dumb ideas implemented to make it worthwhile.

As far as inferior classes of armor, the only reason an "adventurer" would have to use them include economic concerns (cannot afford to have a fitted suit of plate made for them), or dire straits (his plate set was destroyed or stolen, and that suit of brigandine can be thrown on if it’s approximately the right size).  In the case of inferior or bizarre weapons, the only reason a wealthy character would have to use them would be economic or availability concerns, and in no case would a stupid weapon like a bagh nakh be carried onto the battlefield unless the player is attempting to roleplay a suicidal religious fanatic who fully expects to die horribly.