OT impedance and break up relationship

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...Many people today will diode-bias the inputs for this same reason...

Silicon diodes, LEDs etc were common and cheap back when the STR was designed, and I think their use for this application had been established, though it may not have been commonplace or widely known.
But surely the Fender engineers would have been at least aware of the idea, so given the benefits and presumed objectives, why didn't they use it here?