When you see a vehicle and check what gear it holds and find a primary weapon, you can't drag it directly to your inventory slot. You have to bypass this by somehow drop the weapon on the ground then equip it. NOTE: this problem ONLY appears to be with primary weapons.
- Legacy ID
Fix so you can take a primary weapon directly from the vehicles inventory to players.
I experience this issue a lot.
I have heard that if you get in and move the vehicle it works properly.
Otherwise, just drag the weapon to the ground tab, then open the ground tab and drag into your inventory.
It's definitely a bug (maybe already reported) but until its fixed it helps to get on the vehicle on the DRIVERS side, get out again and then you should be able to pick up weapons and the binoculars.