Why do Mazda fake the data?
Because marketing have decided that an oil pressure gauge is required by the 'sporting aspirations' driver at whom their car is aimed.
They have observed that the majority of their owners have no idea what the gauge represents but if the needle is nicely in the middle then the user is happy - until the big red 'oops too late' light comes on...
I have heard of similar tales on the water temperature gauge of certain US cars - they simply switch to 'normal' position after a fixed time and take no account of the actual temperature.
People who actually understand what the gauges are there for, and have the knowledge to interpret the trends they display, are becoming more and more rare.