Yes, I understand using leaded gas in older designs. But what was the manufacturer's excuse to keep designing engines that require leaded gas even on fuel-injected, ECU equipped newer designs?
Not a rhetorical question, I am genuinely curious.
New and old designs have been tested and can work with unleaded fuel. (Edit: there are surely some exceptions here, so I don’t mean this to be all encompassing)
New designs must work with leaded fuel since that is the fuel which is available - until avgas contains no lead this will continue to be the case.
Side note, most new planes are sold without an ecu.
Not a rhetorical question, I am genuinely curious.