The first issue is security clearance in the military. The academic researcher's normal security clearance gives them access to classified confidential information. However, a secret or top secret clearance gives them access to much more information. If people want to access documents that say “Protected A”, they will not have access to all the information, because those documents will be blacked out. These documents are only accessible to individuals with a confidential security clearance.
There is a second problem. In basic training, soldiers, or non‑commissioned officers, are taught that they must never, ever contradict someone of a higher rank. This is instilled in recruits on the first day of training.
If asked by an academic researcher, the soldier will immediately consider that person an officer. The response will not contradict what the researcher is asking for, so the researcher does not really get adequate answers.