Because it's not just people. Maybe organizations, machines, et al. And maybe not one per real life unit.

You've gotta tell 'em! <strike>SOYLENT GREEN</strike> Users / Customers IS PEOPLE! We gotta stop them! Somehow! Listen! Listen to me… PLEASE!!!

call it what it is. isn't that what a good domain model is all about.

- if you have a 'real life unit' call them a person

- if you have an organization, call it an organization (although organization's are made up of people and ultimately it's people in the organizations that will be accessing your application, so you're back at person there too)

- if you have a machine, call it a machine

And if you have a thing that can be used by a person, an organization, or machine, what do you call it?

- Agent - Entity - User - Principal