Screw open his laptop when it's turned off and he's away from home, install a keylogger into the bios. Put a camera onto the shelf to film which keys he types to log in. If he puts a blanket over his head: solely rely on the sound each key makes. Hack his computer remotely using one of the government owned 0days and dump the keys. Use side channels to attain the password via the power outlet in the neighbouring house.
They had countless ways and they chose the one that revealed the least about their capabilities.
FDE's not worthless. Again, I don't think it's even optional; one of your laptops is eventually going to get stolen, and you're going to want the reassurance that at the very least, once it loses power, the thief won't have access to your data (meaning, in effect, that most thieves will never have access to your data). And it's somewhat more powerful on phones, which have integrated designs to make FDE more granular.
But the idea that of all the things the USG could spend energy on, aftermarket FDE software would be their target? It's not very plausible.
> It wasn't even a speed bump for the Ulbricht investigators.
Are you talking about the situation where they had to very carefully snatch a running laptop from a suspect so that they can't lock it? Seems to me like FDE would have been at least a significant speedbump had they not circumvented it. Why else would they go to such trouble? And what would they have done if the suspect hadn't used his laptop in a public place?