Belt drive fixed

It's because a cyclist can develop a lot more torque than a motorbike engine.

Now considering that a Ducati 996 motorbike produces 93Nm at its maximum.
Now a 70kg cyclist standing on the cranks will be developing 9.8x70x(17/100) 116.62Nm

Because the sprockets they are applying this force to are almost equal radius (a 996 comes with 15 tooth sprocket as standard) it means the cyclist will be creating more chain tension.

isn't it 93nm at the flywheel and therefore CONSIDERABLY more after it's been shot through the gearbox? Reducing the silly 9000 or so RPM to something more usable, and more torque-y