Because people want a call stack when an exception is thrown, so they can print it out, just the same way they do in JavaScript and every other language. EDIT:

Because people want a call stack when an exception is thrown, so they can print it out, just the same way they do in JavaScript and every other language. EDIT: Also as another commenter mentioned, this is a property exposed by the VM engine to the host environment, not something directly observable from within WebAssembly itself.