Visible crew/equipment: When Sam falls on the sidewalk with the cube and the machines start coming alive during the fight scene in the city, a fast shot shows a cameraman with the camera on the hands on the right side of the screen. (02:02:16)
Visible crew/equipment: When Sam is at Bobby Bolivia's cars dealership intending to buy the Chevrolet Camaro and all the cars' windows explode, as the camera turns around a shocked Bobby Bolivia the shadow of a boom microphone is visible on his face.
Visible crew/equipment: When Sam is brought by his father to the Porsche's dealership at the beginning of the movie you can see the camera car reflected on the building's glass while chasing them.
Continuity mistake: The number of the surviving ranger team changes, as Keller announces the base attack a shot is showed of 8 rangers and Mahfouz (the young boy), then as the team is attacked by Scorponok one team member is killed, but seconds later as the team runs down a dune they are still 8 rangers. One runs past the camera quickly while 7 and Mahfouz comes down the dune, later as Epps directs the air support he claims they are only 7 rangers, and as the Huey lands there are only 7 rangers.
Revealing mistake: Near the beginning Shia and Megan Fox are driving in Bumblebee, before it breaks down. There is no road shown in this entire scene, no matter which angle you see. No landscape either. This indicates the scene was probably shot on a soundstage and the car was not moving. It is also obvious there is no wind coming in through the windows.
Chosen answer: There is no reason to think they can't. They simply choose not to. They may feel it's too deceitful.
Actually in this movie (when joining up with bumblebee and the others after they pick up the All Spark) and Revenge of the Fallen, Ironhide uses holographic humans in his cargo bed. Also, Arcee and the twins use holographic drivers at the beginning scene in Revenge of the Fallen.