I made this pretty quickly: http://kuuv.io/i/L4rZomr.png Slower than if I just used Python with tkinter since I wanted to learn a new UI framework with Clojure at the same time... But it's literally just a dropdown and some buttons wrapping some system calls to 'gpg'. I never bothered with the 'decrypt file' since I can remember 'gpg --decrypt' easily enough. :)
So I agree using GPG isn't very hard, it's easy to make it even easier for yourself, and I think its usability flaws are overblown. Unfortunately as a comment further up said "the GPG CLI acts exactly as I expect it to...and I don't expect non-advanced users to use it." Only advanced users use the CLI these days. Not because it's particularly complex or hard or a poor experience, they're just given no reason to, and no training even if they had reason.
A GUI that wraps some system calls is how you end up using "p" for all your passwords. One of the many symptoms of OpenPGP not getting the investment it deserves and sorely needs is that there is no production-quality library implementation going.
A better implementation would be nice except that it requires a ton of specialist skill to get right. Plus lots of time. A wrapper is basically an interface. Getting interfaces correctly can be done by knowing what it expects, what properties should always hold, and what happens after each call. Correctness is basically one or more state machines with assertions built in for interactions between front end and library. Much easier.
So I agree using GPG isn't very hard, it's easy to make it even easier for yourself, and I think its usability flaws are overblown. Unfortunately as a comment further up said "the GPG CLI acts exactly as I expect it to...and I don't expect non-advanced users to use it." Only advanced users use the CLI these days. Not because it's particularly complex or hard or a poor experience, they're just given no reason to, and no training even if they had reason.