1. Military regulations: The military can buy gold, but it needs to comply with relevant regulations and procedures.

2. Trust relationship: There may be a trust relationship between you and the soldiers. They think you are trustworthy, so please help buy gold.

3. Special benefits: The army may have some special benefits or treatments, such as buying gold and getting discounts or concessions.

4. Political factors: There may be political factors, such as contacts or cooperation between the military and the government.

In short, there may be many reasons why soldiers ask you to help buy gold without your money, which needs to be analyzed according to the specific situation.