The problem is running the wire from the front door to wherever you put the transformer and the transformer has to plug into your home wiring to get juice
It is easy to do when they are building a house, as the walls are all exposed, but once the sheet rock goes on, its another story. I have a newer house and they did not wire for a doorbell as the builder installed a wireless doorbell. The button that was on the outside of the door had a battery that lasted 2 or three years and then you just popped in a new one. But no camera.