Could you imagine fitting a 'Differential' to the axle of every rail vehicle to allow the wheels to turn at different ratios on a curve?With an Aussie flag on the front if I recall.
The weight and structure alone plus its something else to wear out and break down to make it hideously expensive to use.
The 'Differential' effect is achieved by angling both the head of the rail and the wheel face and of course wide curves.
Some years ago a Dutch company call DAF made a small vehicle that used 2 cones and belts to achieve a clutchless almost infinite number of 'Gears' as well as allowing each wheel to rotate at its on speed on a curve.
This system is still used on Ride On 'yard' tractors used for large area lawn mowing today.
BTW, in the DAF Company museum in Holland is a small van that was driven from Cape Town in South Africa to Amsterdam using this drive method.