Being able to collate the requisite inputs from outside sources is the real problem. If you can’t do that reliably it’s simply hard to build an algorithm around it. Flights for example would require your calendar program to reliably pull data from an API regarding the flight information that is current and effectively real time. That’s the actual hard part, and this expands across services.
For all the advances we have made with computers and smartphones in particular they suck at meaningfully exposing a way to collate data sources and create actions around them reliably
Having one running locally helps but it's still necessarily storing information that you might not want to have stored where someone could potentially retrieve it, either via some sort of exploit or by forcibly compelling you to give it up.
That years of training is what we are missing. I don't think modern AIs can be trained in the way the assistants of old could be, at least not yet.