Nearly half the prosecutions involved the use of informants, many of them incentivized by money (operatives can be paid as much as $100,000 per assignment) or the need to work off criminal or immigration violations.
Sting operations resulted in prosecutions against 158 defendants. Of that total, 49 defendants participated in plots led by an agent provocateur--an FBI operative instigating terrorist action.
With three exceptions, all of the high-profile domestic terror plots of the last decade were actually FBI stings.
In many sting cases, key encounters between the informant and the target were not recorded--making it hard for defendants claiming entrapment to prove their case.
Terrorism-related charges are so difficult to beat in court, even when the evidence is thin, that defendants often don't risk a trial.