I remember reading somewhere on this sub (I can't find the post unfortunately) that mesoamericans like the Aztecs were capable of ironworking but did not use iron weapons because they quickly rusted in the humid climate of Central Mexico. If that is the case, why did metal weaponry persist in old-world jungle climates like Southeast Asia?
A follow up question about why ironworking persisted in SE Asia: what is the functional value of a keris over other weapons? Its relatively straight shape appears to make it about as good for thrusting as a straight-edged blade but does the wavy blade design significantly add to the cutting power of the weapon? Is this primarily an adaptation to the hot climate? If making the blade wavy improved cutting power substantially, why did this blade design remain primarily in SE Asia? Is the design mostly there for aesthetic and intimidation factors?
The lack of iron in Pre-Columbian Americanism has nothing to do with climate. Central Mexico is in fact quite dry, being a high plateau, and the local vegetation is mostly scrub-brush, not jungle.
Ironworking technology was extant in both China and India by around 2000 BC, and seem to have spread to the Southeast Asian Mainland (with attested sites in modern Vietnam and Thailand) by around 400 BC at the very latest. Other sources say it's not clear when iron-working was introduced to SE Asia, but it seems to have been well established by sometime in the First Millenoium AD, since we find trace of iron artifacts in the Buni culture sites.
My understanding is that the wavy blade of the Southeast Asian kris is largely aesthetic or spiritual rather than functional -- most kris from before 1500 have straighter blades.