As Hiraku said, APD officers are permitted to move vehicles to the side if it is obstructing some sort of pathway. I understand why you are questioning this, but try to understand that you have all the time you need to set up and you have a short amount of time to successfully rob the bank. The APD has to push you in order to ease the tension, and if we had to lockpick your vehicles, the bank would be EVEN MORE overwhelmingly rebel sided, considering you have higher ground, key defensive positions, 7.62 rifles, grenades, and more.