True, but.
Mirrors are less prone to failure than cameras.
Mirrors can be broken. So can cameras, but cameras are also prone to power issues, display problems, cabling issues, interference (wireless cameras) and a host of other things that simple mirrors are not bothered by.
To use an old example - The more complex the plumbing, the easier it is to back up the toilets.
For that reason, I do not see them being discarded.