Because on non-English keyboards curly braces are a pain to type. E.g. in Danish it requires Alt + Shift + 8 (on a Mac), and if you look at the comments above y

Because on non-English keyboards curly braces are a pain to type. E.g. in Danish it requires Alt + Shift + 8 (on a Mac), and if you look at the comments above you'll see that the problem is the same for many other languages.