That's been one of the big drawbacks and criticisms of the debriefing after trial: that jurors, particularly after a long trial or a trial that's been particularly difficult, are usually exhausted and just kind of numb from the experience. As to having that debriefing immediately after the trial, many of them can't appreciate it, and they walk away from any of the benefits. They'd really rather not be there.
Typically, it's maybe a couple of days later or a week or so later when they realize that, yes, that case is still bothering them. They're still thinking about it a lot, maybe having nightmares about it, and finding that their blood pressure is up. They realize at that point that they need some additional help, as opposed to immediately after the trial.