Q: Why are biped robots hard in 2019? (COTS motors, sensors, off-board power)

This Robotics Stack Exchange discussion seems pretty good:

https://robotics.stackexchange.com/questions/10616/why-is-it...

This one, less so:

https://robotics.stackexchange.com/questions/8129/why-are-bi...

Apparently people are interested in the question, but no one is answering. Hmm.