[danvet]

It doesn't because it isn't ;-)

In real sword fights the defenders jobs is to deflect the attackers stroke (more or less). If you'd just try to stop it (physically reversing the attacker's impulse) that would either not work at all (because you don't have strong enough muscles) and the sword would still hit you. Or equally bad, the sword or your bones break due to mechanical overload.

Now according to the description the robot simply pulls back if it hits resistance, which results in the fake looking moves. Deflecting a stroke probably wouldn't work because of the robot's mechanical structure is much more rigid than a human's.

Slow-motion sword combat works/looks much better if the fighters are aware of how it actually works when not simulating the moves.

Amend: The "physically reversing the impulse" is a bit hand-wavy. You just have to put an equal momentum into your own sword directly opposing the momentum of you opponent's sword. Now if your attacker goes in for the long haul, he has about a meter of movement to put the momentum into his sword, whereas the defender usually has much less. This therefore requires much more force resulting in the above consequences.