GPG is a open source implementation of PGP public key cryptography. It’s intended for use for things like signing and encrpyting emails. But it simply hasn’t caught on with most users.
Instead of developing opinionated software with a simple interface, GPG was written to be as powerful and flexible as possible. It’s up to the user whether the underlying cipher is SERPENT or IDEA or TwoFish. The GnuPG man page is over sixteen thousand words long; for comparison, the novel Fahrenheit 451 is only 40k words.
Given the small user base, replacing it with something more usable shouldn’t cause much disruption. But what?