To answer the question, as to why the military didn't send condolence letters, it's because suicide is considered cowardice and the military doesn't reward cowardice, or any other substandard behavior. Soldiers who commit suicide dishonor themselves, their unit and their service.
The Pentagon disagrees with you. The military didn't send letters to their familes because they feared it would encourage more soldiers to commit suicide.
As I pointed out, some peole think that mental illness is a character flaw. Some of these people are so deluded that they imagine the Pentagon shares their delusion