Mirrors pretty much always "work". Cameras can stop working. Technically a video screen you're viewing going down the road to watch your camera may be a violation of the law.
What happens when you want to pull a different trailer? Do you move the camera? Maybe you only have one trailer but I have at one time owned a cargo trailer, a flat trailer, and a boat trailer.
Is the camera wireless and battery powered? What happens if the batteries die?
If it's hard wired then you have an extra cable to hook and unhook, what happens if it comes un-done.
Mirrors beat cameras any way I can think of.
2005 Chevy CC Dually D/A, 2003 Fleetwood 11X truck camper, 1997 Larson 206SEI boat