What do you think Firefox calls it?

The same, for the same reason

Isn't it just a name?

A user can easily enable the developer tools if needed, same way I'm not a mechanic but can open the hood of my car.

You can open the hood of your car, but there’s probably not much you can do there.

Of course I can. Add cleaning water, check oil levels, replace a light bulb. No much else I can do, but others may, and other won't even do any of this.

Point is, this is not a binary choice. Between user and developer there are many people with varying skills that will use a user-agent switcher if needed.

It’s not about capability, it’s about interest.

Most people could do a bit under the hood of a car, but they simply don’t care.

It’s the same thing with computers. Most users are savvy. They just don’t care.

In my experience (systems engineer/devops for both Windows and Linux for more than 25 years), very few users are actually savvy. Even those working in tech.

Our definition of savvy probably differs.

That is possible. Mine would be more or less "someone who knows what they're doing"