Why does a UI have to have personality? Why can't it just look good and be easy to use? Does anyone actually care if an application is "speaking" as if it is a conscious entity?

It depends on the application.

For a tool that you use as often as Gmail, you want something functional, but that doesn't mean it can't let the personality of Google shine through. Gmail's empty spam page says something like "No spam here, Hurray!" where as Outlook's says generic and bland like "There are no items in this view".

However, consider a shopping experience that you may use a couple of times per year at most. The application has a real opportunity to expose the user to your brand.

Also consider a new user experience that you only ever do once. These processes are boring, so maybe some personality helps conversions and reduces falloff.

There is no right answer here because there are so many different types of applications.

> Why can't it just look good and be easy to use? Does anyone actually care if an application is "speaking" as if it is a conscious entity?

I don't think it's fair to say that a UI shouldn't attempt to have some "personality". Whether it is ultimately effective (or not) is another argument entirely, but there is more to UX than just the style and "ease of use".

Copy, labeling and alerts are all part of the UX too.

Good UI design is all about effective communication. If you have a UI that is pretending to be something it isn’t (a person) then it is basically lying to you. That’s hardly good communication. It’s confusing and dishonest.

And believe it or not there are some users who won’t understand that it isn’t really a person. Some minds are very prone to anthropomorphizing especially when they are dealing with something they find hard to understand and unpredictable like a computer.

"Having a personality" is going to happen whatever you do.

Somewhat counterintuitively, this doesn't mean your interface pretends it's a person; but all copy is written by people -- words are used by people only (pretty much), directly or indirectly -- and the words chosen are projecting some personality onto the application whether you want to or not.

There are no words/phrases/instructions without baggage, connotations, etc..

I have no objection to that. I just don’t want those words written by people to make it sound like the application is a person. The app can talk about itself doing things (it does do things after all) but not as a human being with feelings and stuff.

Why do most cars still have face-like features when viewed from the front or back?

Yeah, actually even in that case, I'd prefer no pronouns. "Fetching email" is much better IMO, and possibly more accurate (Imagine my girlfriend logged into my email for instance).