Assume every motor has a 1% failure rate per year.
A boring wheeled roomba has 3 motors. That's a 2.9% failure rate per year, and 8.6% failures over 3 years.
Assume a humanoid robot has 43 motors. That gives you a 35% failure rate per year, and 73% over 3 years. That ain't good.
And not only is the humanoid robot less reliable, it's also 14.3x the price - because it's got 14.3x as many motors in it.
[1] And bearings and encoders and gearboxes and control boards and stuff... but they're largely proportional to the number of motors.
For example, do the motors in hard drives fail anywhere close to 1% a year in the first ~5 years? Backblaze data gives a total drive failure rate around 1% and I imagine most of those are not due to failure of motors.