...not sure why Tamiya insists on offering such short gearing on so many of their cars.
Simple. Despite what we'd like to believe to be the case, us racers are not the core market for Tamiya. Casual bashers are the majority of the market and they're happy to run silvercan motors all day long. Short gearing gives just enough zip to make the car feels fast on acceleration while keeping the top end low enough to retain driveability on the (fairly low grip) kit rubber. Also helps run time and doesn't over stress the kit motor.