Because the average person has no idea how to use it? Because both parties have to have it set up for it to work? Because setting it up wrong will grant you n

Because the average person has no idea how to use it? Because both parties have to have it set up for it to work? Because setting it up wrong will grant you no protection? Because it just encrypts the communications in transit but when you're already under suspicion they can grab your computer, which has the unencrypted files on it? Because in a setting like this (trader's work computers) you're often not even allowed to install any software?