As many others has said, having screenshots of the different programs isn't included in the AUR. The priorities of Arch Linux won't be the same as those of Fedora, Mint, etc., as they target a different audience who appreciate a more minimal distribution.

To put it another way, it would be like going to a hot dog stand for a sandwich. They serve hot dogs and intend for them to be eaten by people who like hot dogs more than sandwiches. If you want a sandwich, you would go to the sandwiches stall, not yell at the hot dog guy about why the hot dog doesn't taste like a sandwich!

It provides screenshots, categories and icons for Flatpak packages. AFAIK those aren't provided by AUR or the official Arch repositories. Icons seem to be integrated for some official packages at least.

A Shelly in-built way for user contributed additional data for Arch packages could be a way to tackle this. But that needs additional infrastructure, developers and volunteers who curate the contributions.

Shelly is a nice frontend. Octopi is too, to quickly check PKGBUILDs, show contained files or open the respective AUR page.