We've all seen that label on our passenger side mirrors that says, "Objects in mirror are closer than they appear." Why is this? Further, why does it only apply to the passenger side mirror, and not the driver-side or rear-view mirrors?
The mirror is made convex in order to provide a wider field of view. Thus, the objects in it appear smaller than on a flat mirror, and your brain infers they should be further away.
The reason only the passenger mirror is convex is because you are farther away from it. The angular view provided by farther mirror of the same physical size produces a similarly smaller reflected field of view. The convex mirror provides a larger field of view- one that should be comparable to the closer drivers mirror.
You could instead mount a much bigger mirror on the passenger side and get the same field of view if you prefer a flat mirror.