The actual reason for the plate was a combination of all but principally, to prevent the waste of otherwise perfectly serviceable fore-ends that would have been scrapped due to that part of the fore-end already having been crushed. So you machine out the damaged part, insert a steel plate (that target rifle builders such as Fultons of Bisley had been doing for many years) that will spread the load of the tight FTG screw down onto the trigger guard, onto the plate, then onto a greater area. To be honest, it was a brilliant modification.
Not done to all rifles originally but adopted and codified for production