Because you still need to manage your GPG keys with an obscure CLI. When I last switched computers, I tried just copying my "~/.gpg" directory. Didn't work. GPG was confused, produced even more confusing messages, which didn't really help me understand what the problem was. I needed to google for the right incantation of commands to export my keys from one computer and import them on another. Compare that to what you have with KeePassXC: switching computers? Just copy this single file and everything will just work.

And I don't want to know if I'm holding GPG right. I just want the tool to work for my specific case. But GPG wasn't designed specifically with this case in mind, so, as usual, it will be terrible. It tries to be too many things.