You understand cameras have their limitations? They have blind spots, wireless cams can be hacked, wired cams can be compromised, they often do not detect for numerous reasons and some have lag times, they can be affected by weather/power issues, etc...Furthermore, bad guys nowadays are emboldened and most don’t care about cameras, and they wear masks, hoods etc. Also, not everyone can afford these systems.
Btw, I too have audio/video cams as well as other security assets, so I understand what they can or cannot do. Bottom line, someone banging on your door in the middle of the night might be there trying to save your life, warn you etc. Ya never know.
Those systems are very affordable and while they do have their disadvantages, they can be minimized - and certainly are a better option than coming to answer the door in person.