I've dug up some old/new post on this and knoe that i can jump the wires or buy a usdm solenoid+oil press-switch if using a usdm p72 ecu. Why did honda not use vtec oil pressure switch on JDM obd2 motors?

I have a 96 jdm b18c and usdm p72 and i knoe what my options are of getting no cel. I just want to knoe why its not on obd2 jdm motors unless like someone said this function is in the ecu.