Marc Raibert was a student of Ivan Sutherland. Sutherland had a lot of pull at DARPA. This facilitated the unique prototyping work done at Boston Dynamics to get noticed and supported by DARPA.

But as a flip side of this, Boston Dynamics developed certain idiosyncratic interests in getting the hydraulic valves just right, etc. Their machines required a lot of tender care, (expensive!) and were dangerous to be around.

When Google acquired them, many things were mismatched. Andy Rubin, the VP at Google who advocated for BD, got fired for alleged sexual misconduct. This cast a shadow on the whole plan that he was trying to implement. DARPA finding did not sit well with Google's ethics. They pushed BD to stop getting grants from DARPA.

Expensive and dangerous robots were not an ideal fit for AI experimentation. Google was buying cheap and much safer tabletop robots for that. All in all, there was no good fit, and after spending tons of money on it, Google have gotten rid of them. They did encourage BD to develop a cheaper, safer electric robot, and this became Spot Mini.