That’s just ergonomics.

You are shooting with a long lens. Unless you have the camera on a tripod/monopod, it’s much more stable to have the camera braced against your body with the viewfinder up against your eye, versus trying to hold 5 pounds of very long lens at arm’s length.

(Nikon 200–500mm lens in this case. Trust me. Way easier to support that chonker when it’s held close to the body when running around to shoot rugby.)

On many cameras you can set the viewfinder to match the prescription of your eye-glasses. I need glasses to see data displayed on the rear screen, but can easily read the viewfinder data without them. Saves a lot of faffing around

Exactly the opposite for me - possibly für to astigmatism, I only use the rear screen, as then I can use glasses, but I don't see sharply through the viewfinder and with glasses it's just uncomfortable.

My wife is a pro, she's actually in a bit of a hole over this issue.

Her eyesight has changed, the focus correction on the eye piece is not working well for her now (it has limited correction range) and her glasses are in the way. Using the back screen is difficult outside because of the sun and speed. Also strength; holding a camera with a big lens at arm's length all day is hard for her.

So - contacts, which she hates and her eyes react badly to.

She might have to pack up, which would be very upsetting for her having built a business and because she get's a lot out of her work.

The sun can both outshine the brightest screen, and blind the photographer's eyes. Using a viewfinder avoids both those issues.

The alternatives in strong sunlight would be a rigid hood around the screen (which exist as accessories), or a fabric hood covering the screen and photographer (like what early photographers used).

I would guess it has to do with zero latency.

And possibly easier aiming/coordination/stability with the camera and hands at not just eye-level, but also nearly right up against the eye, moving in unison with one’s head. Just a guess though. Sports television cameramen seem to do just find tracking the ball without using a viewfinder.

In this particular camera and many other mirrorless cameras, the viewfinder is another digital display. My guess would be they’re required for making it easier to focus in direct sunlight. I tend to only use the viewfinder in this situation (on an a7s ii and a1)

It’s also much more difficult to hold a camera at arms length to view the screen.

When you hold up a camera to your eye and use the viewfinder - it’s a third point of contact. You’re also using your face to stabilize it.

Trust me - they’d get rid of the damn viewfinder if it wasn’t often requested so much. Using the viewfinder is just a lot easier than the back of the screen in many situations. (Especially outdoors. Think about rain or whatever else going on getting on the screen)