The individuals that are engaging in combat action with the military forces of nation-states currently are not members of the armed force of any nation.
Being captured on the field of combat results in detention. Said detention, during the time of conflict, does not grant anyone a trial. Such individuals are typically detained until hostilities cease.
As such releasing anyone before cessation of hostilities is actuially quite compassionate. That compassion has revealed that in many cases it was misplaced as the very same individuals were again caught engaged in combat action against uniformed personnel.
I make no protestations as to guilt or not, that is not my purview. But if they are engaged in combat action against troops detention is a valid response.
You dismiss humane treatment as immaterial, yet the treatment received by inmates of the detention facility is far better than that a prisoner can expect in any CONUS prison. Your fixation on the efficacy a trial to accord proof is sorely misplaced. The US justice system is not balanced, nor is it concerned with justice.