Because an eye exam isn't just about the final prescription. It's about whole eye health (retina health, cancer, cholesterol, diabetes, etc).

Right, but then the way to do that should have nothing to do with corrective lenses and requiring them shouldn't be an artificial barrier to getting corrective lenses.

If it's important, then it's important for everyone.

This is important. Eye exams are not just the part where they have you look at letters on the wall in the dark.

The machines can't gauge for personal preference. Many people don't like their vision right at 20/20. I personally like mine closer to 20/15.

What? Doesn't 20/20, 20/15 etc. refer to visual acuity (how much detail you can see from a certain distance)? Are there people who prefer anything but the highest possible visual acuity?

This I think has a lot to do with individual experiences with optometrists. I went to probably half a dozen optometrists since adolescence before I happened to end up with one who actually made it clear there's a degree of subjectivity with an eyeglass prescription.