As far as I know (correct me if I’m wrong), for a mechanical wave (e.g. sound), the frequency determines the pitch, the amplitude determines the loudness, and the amplitude is proportional to the intensity, which represents the energy the wave carries.
In an EM wave like light, the frequency determines color and energy, the amplitude is simply the amplitude of the E and B fields, while it is the intensity that determines brightness.
Why are the roles of the same factors different in these two waves? Why does the frequency in light influence energy but not in mechanical waves? Does frequency or intensity determine energy in a light wave?