The 8 who conspired to kill Lincoln were acting as militants; and martial law was in force in DC at the time. And the 8 who FDR tried were acting against the country during a real shooting war. It's not the same.
Something is going to have to happen to allow the government to claim the the civilizing courts are non-operational or unsuitable for trying these people who were behind the failed coup. We don't know what that is yet.