This was also an issue in ArmA 2 by the way.

Currently it is absolutely impossible to reliably attack infantry/buildings and it is extremely complicated to attack empty vehicles and vehicles that belong to your faction but are driven by enemy soldiers with fire and forget missile such as the missiles of the KA60 simply because you neither have the possibility to guide missiles manually with your mouse nor you can simply press "Tabulator" to automatically guide > lock on missiles to empty and "hijacked" vehicles, you would have to aim at them with your crosshair and press your right mouse button which is extremely annoying in certain situations.

In my opinion this is just unlogical and generally unrealistic due to the fact that all modern attack choppers are also capable of manually guiding their missiles,for some it is even mandatory, however on the ArmA series it is currently only possible to use "fire and forget", except for one instance:
All MI24 helicopters in ArmA 2 were able to either let the gunner use fire and forget or manually guide missiles to the target, it increased the versatility and immersion of this chopper a lot.

My suggestions on what should be changed:
Make it possible to lock your missiles onto empty and hijacked vehicles by just pressing Tabulator.
Add a camera which allows it to guide missiles manually to all choppers and jets that are capable of carrying missiles, the camera could be controlled by the co-pilot while the pilot is flying or vice versa, in case of single seated jets I would suggest to add so called "targetting pods".
For that please look at issue: 0007502