But "these people" are also "most people". "Most people" also don't use PGP, for many reasons, but IMO chiefly that it's hard to manage keys without outside (centralized) help. If Google managed PGP keys for you, there'd be little problem with muggles sending and receiving encrypted (albeit insecure) email.

Since Bitcoin needs a critical mass to be successful, centralized exchanges and wallets are needed to build it up so it's generally useful.