Earlier quoted context omitted.
On the other hand, a 100:1 gearbox gives you much-needed torque if you're lifting a load at the end of a long arm, it makes your encoder 100x more precise (in terms of repeatability) and it makes your motor brake 100x stronger. Back-drivability is the enemy of precision, so many robotic applications can do without it.
Almost all modern servo driven units I've seen prefer to allow some compliance in the end effector. The UR5 and UR10 series for example can use force limiting control loops, and are safer to use around people. The old "fast, cheap, or good... choose any two joke is mostly still true. =3
You’re right that it has a freedrive mode, and force control modes. But it’s a rigid, low-backlash robot with the compliance achieved in software afterwards.
Expensive, naturally, but none of the problems that come with things like series elastic actuators.