I’m sure they spent 24/7 with a cuirass in the Central American heat. Also, not every Spaniard in those expeditions had the money to buy one for themselves.

EDIT:

Was the United States trying to kill all the Afghanis,

No, neither was Spain in America, since the natives could be captured as slaves

raise the Stars and Stripes over Afghanistan and start mining and farming the place for goods to ship back home?

Pretty sure that ended up being one of the things during the occupation, yes.