The purpose of CarPlay is to integrate apps on the iPhone with the car's native hardware (steering wheel buttons, infotainment display, speakers, etc.).
If you're willing to stick your phone to the dashboard and to use it directly, without any car integration, then why do you need CarPlay? You can simply open any app you need and use it normally. Not to mention that you'll get the full functionality of the phone, without being limited to just a few select apps and to just a fraction of their standard features.