But normal people have entirely different problems than rich people do! The amount of administrative overhead that would warrant a personal assistant is just vastly lower - most normal people:

  - don't travel frequently, 
  - don't have so many complex inquiries that require someone to research,
  - don't have super complicated taxes to file, 
  - don't go eating out in fancy restaurants that require special skills to get reservations in, 
  - don't have so many meetings to attend, 
  - don't receive hundreds of emails per day,
  - don't work on multiple projects at the same time,
  - don't organise festivities and social gatherings all the time. 

Yeah, there probably are some things that could be simplified by delegating to someone, but they don't justify a human PA at all; and out of the remaining tasks, most are not really digital in nature: Going for groceries, doing chores, child and elderly care, interacting with other people, and so on. Digital assistants can't help you with any of these.

The one thing that would be useful - a kind of "chief of staff" that monitors your entire digital life and prioritises your every next step - is the antithesis to Siri and the like, which are merely reactive to your requests, not proactive in figuring out what needs your attention next. Let alone that that would be a total privacy nightmare, and a prime candidate for mass manipulation at scale.