The 1%/year failure rate appears to just be made up. There are plenty of electric motors that dont have anywhere near that failure rate (at least during the expected service life, failure rates certainly will probably hit 1%/year or higher eventually).

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.

To an extent, yes.

For example, an industrial robot arm with 6 motors achieves much higher reliability than a consumer roomba with 3 motors. They do this with more metal parts, more precision machining, much more generous design tolerances, and suchlike. Which they can afford by charging 100x as much per unit.

Yes but like almost everything it comes down to cost. Most consumer devices are extremely cost constrained. Industrial robots can justify higher costs that come with higher reliability.