I really don’t understand how a four wheeled self-driving powered vehicle is allowed to drive on the sidewalk when riding a bicycle on the sidewalk in that same city is illegal.

Probably under the same regulations that allow a powered wheelchair on the sidewalk. A low maximum speed makes up for a lot of things. But they should have a plan for encountering a wheelchair user.

Because traffic laws work for cars and pedestrians. Anything else in between in fuzzy and hard to define or legislate

Because corporations have more rights than the common man and these robots are the property of corporations.

If you as a regular person cause some sort of damage to a corporation you’ll be arrested and locked up while they determine the legality and if there was an actual illegal damage. If these corporations cause regular people problems then it’s “oopsies, you can sue us in court with your far smaller resources in a system that is heavily incentivized for those with more resources” and no equivalent corporate entity is getting the equivalent of cash bail.