Because designers fuss a lot about nearly undetectable differences in color, fonts, and many other things. Maybe they make a difference in the aggregate. But if you can’t identify the difference between Ariak and Helvetica (to pick a particularly glaring example) you’re probably not one of those designers.
No idea which one it was but I found this one and got a perfect score. The difference is pretty obvious... https://www.ironicsans.com/helvarialquiz/index.php
Same, 18/20 for me. The all caps on MATTEL got me, and the STAPLES one as well, for some reason.
But the differences on the lowercase "t" and "s", uppercase "g", the number 3, and both upper an lowercase "c", are obvious. Helvetica is much more refined.
There are good reasons why well designed typography is expensive. A lot of thought and effort went into designing every line and curve. Even if most people can't consciously appreciate these details, they experience it subconsciously by how the design makes them feel. This is why brand designers are well paid. Anyone can design a logo, but to make a design that transmits a specific feeling, that requires a lot of skill. And typography is a core component of this.
I agree. Many people can hardly tell the difference between Arial and Helvetica. There used to be a website where you could test how good you are at telling them apart.
You won't notice many small differences between certain fonts. But that doesn't mean they're unnecessary. As you said, they make a difference when taken together. For screens, there are a number of adjustments and techniques that improve screen readability. Hinting, separate designs, contrast for low dpi and subpixel rendering compatibility, for example. At least some of the optimizations don't work out of the box, but have to be adjusted by designers. That's why it can happen that a font you bought for print media now requires an extra license for websites and apps.
There are plenty of wonderfully readable fonts for the web and apps that are free and sufficient for most projects. If you want something special, I don't think it's wrong to pay for it. Personally, I would prefer more reasonable prices, though.