You should think about it from a legal perspective: if you use GPG, will the FBI show up at your house just because the local drug dealer also does even though they never send you a message?

Now, suppose that there’s a transaction chain which involves you – say said local dealer buying from one of the few other people using it — and how you’d prove that you weren’t a knowing participant in some sort of laundering scheme or deal. This is why tumblers aren’t likely to be used by most people and why running a Tor exit node is so risky: you have to worry about being charged with the worst thing done over the network and proving that you aren’t just trying to look like a naive user.