Fundamentally the things you want from a secure crypto system differ depending on the context in which you're applying it. Email needs different things than package signing does than file encryption does. It's silly to pretend that the same tool can provide a good and secure experience for all of them.
Take forward secrecy. This is a property that means that if your key is compromised, it doesn't allow breaking everything you've done with it. This is a very desirable property for email or messaging because you don't want somebody reading all your conversations if somebody ever gets their hands on your key.
Or take non-repudiation. This means that when you sign a message you say "John Smith did this", and John Smith can't deny having done it.
For email or IM we want forward secrecy. You don't want all your conversations to become readable if anyone ever gets their hands on your keys. If you're caught, you don't want the authorities to be read your entire conversation about obtaining drugs, you want a system such that even if they get your phone, they still can't decrypt your captured encrypted messages. GPG isn't capable of this.
For email or IM we don't want non-repudiation a lot of the time. If you're caught, you don't want every message being "Signed, John Smith". GPG provides non-repudiation, which is undesirable.
On the other hand, we don't want this for package signing. We want to know that John Smith released this thing. We want to hold John Smith to account if he signs a malicious package, that's the very point of John Smith signing it.
Things might be different for a relatively insecure medium like IM but the same principle applies. Most IM users keep their old messages around thus negating the value of forward secrecy.
>For email or IM we don't want non-repudiation a lot of the time.
We might not, but the people we send our messages to will want to prove we sent it. Otherwise you open yourself to harassment and general abuse. If you don't want to sign your emails then you don't have to. Deniability through claimed forgery doesn't really work anyway:
This apparently almost wilful ignorance of the context of the "data with some attributes" is (specifically, how it's used), arguably, part of the problem.
It's been how many years, and still no-ones' written a good interface?
Using PGP with disposable keys.