They really didn't fall short. A lot of people who would've had assistants no longer do, now it's really just the executives like you said. But fairly low managers used to have them and now they don't.

Software is pretty good. It remembers everything, perfectly, forever. It will never forget to remind you of something. It can give you directions, sort your emails by how important they are, help you find shops and restaurants. The only people busy enough to warrant an actual human doing that stuff are executives. And, even then, I think for most of them it's an ego thing, not an "I need this" thing.

The purpose of a personal assistant isn’t to fit people into your calendar. It’s to filter them out. They serve as a barrier to your time, not an enabler for other people to claim it. I don’t see how an AI can meaningfully accomplish that any better than simply just making yourself more difficult to reach.