This falls into the category of "differences in prepositions that cannot be explained." Prepositions are notoriously hard to translate because they are used differently and in different contexts in various languages. You just have to memorize that "exchange something for something" in English becomes "échanger quelque chose contre quelquechose" in French. I know it's not a satisfying response, but I hope it helps!
(and as a side note, it is possible to say "CHANGER quelque chose POUR quelque chose," which demonstrates just how the preposition depends more on the verb being used than the meaning being created)
'swap' is not a slang word.
Word Origin and History for swap (v.)
c.1300, "to strike, strike the hands together," possibly imitative of the sound of hitting.
The sense of "exchange, barter, trade" is first recorded 1590s, possibly from the practice of slapping hands together as a sign of agreement in bargaining.
The noun in this sense is attested from 1620s.