A slow moving robot on a sidewalk in the worst case makes it inconvenient for pedestrians, and robs the rights of those in wheelchairs etc.
A medium speed robot in the bike lane in the worst case causes a fatal or broken-bone accident.
I think you’re right that liability concerns are probably what motivated companies to design for sidewalks instead of roads. That being said, I think it’s very unlikely that a robot weighing 100 lbs and moving 15 mph is going to kill anyone. Could certainly cause some property damage or break a bone, but is that worse than blocking a disabled person on a sidewalk or pushing deliveries into full cars?
True. I don't think they belong in bike lanes nor pedestrian-only sidewalks.
These delivery companies are being subsidized by our already-limited pedestrian infrastructure.
Also, no human should have to move out of the way or trip over some someone's burrito delivery robot.