it doesn't have to. only if you want to use it's built-in vpn. instead, use your regular vpn, and open orbot, go to settings, make sure ''start orbot on boot' is ticked. if you can't tap connect, then tap connect from your notification message and you're good. it will auto-connect after that so you can use it as a tor proxy for other apps while staying auto-connected to vpn 😉