To be fair, making a robot to fix a specific kind of dishwasher whose internal layout is known and where fixes involve replacing parts already meant to be replaceable is probably a lot easier than one that can fix any dishwasher. Same with sorting trash.

The big point here is that this boosting and potentially servicing mission isn't being pitched by NASA. It's a SpaceX proposal connected to their entirely private program to develop EVA capability for Dragon and to eventually test Starship's ability to support crews in space. Thus for NASA it would likely be cheaper than if they were asking for it.

So the reason we likely won't see a robotic servicing of Hubble (from this) is that it doesn't have as much relevance to SpaceX's goals with Polaris Dawn as just docking, orbit raising and maybe crewed servicing does.