Well, we also use the dollar sign to signify a variable in bash and PHP even though we aren't talking about an amount of USD. Likewise we use single and doublequote to mean special things.

HTML tags have nothing to do with less than or greater than, yet here we are.

In conclusion, it's simply convenient to use the standard keys we have and to use the symbols that are on it to mean something different from their original meaning in order to be able to express ourselves succinctly so that we don't have to spend so much time typing as we'd otherwise have to.

Of course you could always buy yourself an APL keyboard and write your programs in APL and use an APL REPL as your command line instead of using bash ;)