You also asked 'Why' the USMC bought 185 SWC 35 ACP. Who knows? Maybe it was an itch that they had to scratch. Maybe the GAO can devine the answers.
I don't care why they chose/bought the 135gr .40, in fact, if I carried a .40 I'd probably buy some of the overrun. Good ammo at a good price.
To me the bigger question is WHAT'S THE USMC DOING WITH A 35 ACP? Velocity? Weight? Can't be used by the enemy? I WANT TO KNOW!!