Why do some brokers only have bank wire as fund deposit and withdrawal?

Going to sign up for thinkorswim account and it’s not only fx but has everything else like options, equities etc but it only has bank wire transfer as a source of funds deposit and since i am not from the US i would need to get my bank to do conversion to USD.

Why doesn’t thinkorswim use paypal to fund and withdraw? Is it cos it isn’t “professional” enough?