Continuity mistake: When Ron and Sam, followed by Bumblebee, make the U-turn in front of Bobby B's and then park, the spinning 'Bobby B. sez...let's talk deals' sign is to the left of the three vintage gas pumps, near the clown. When Bobby B. puts his arm around Sam's shoulder and says, "Sam, your first enchilada of freedom..." the spinning sign is now on the other side of the pumps, where there wasn't a spinning sign previously. (00:12:10 - 00:13:15)
Continuity mistake: In the scene where Sam is being interrogated at the police station, the cop catches the drug bottle with the bottom facing up. When it cuts, the top is facing up. (00:38:20)
Continuity mistake: At Hoover Dam, when Sam tells Banacheck the terms of his cooperation (which include expunging Mikaela's juvenile record), Mikaela's high-gloss lip gloss disappears in her close-up, then reappears. (01:36:00)
Continuity mistake: When Bumblebee's legs are destroyed, as Sam leans over in front of him and asks if he's alright, Sam wears blue patterned boxers, but when Lennox runs up to Sam, who is standing on the tow truck helping Mikaela hoist Bumblebee, Sam's boxers are grey (as seen between his white tee and jeans). Then, when Sam is on the roof running, after the chopper is hit, his boxers are blue patterned. (01:53:45 - 01:57:10)
Continuity mistake: As we are hearing Prime explaining, "They're a young species, they have much to learn," we see S-Seven's SUVs pull up to the curb at Hoover Dam and the doors open, right beside the vertical guardrail posts with the horizontal beams. In the next close-up, all of the horizontal beams have vanished. (01:34:25)
Continuity mistake: When Ron (holding a flashlight and lantern) is looking through Sam's bathroom window, saying, "Judy, better call the city. We got a blown transformer...," there is no windowbox under that window, which was there earlier. Yet when Prime says "Ironhide, you know we don't harm humans! What is with you?" the rather large windowbox full of flowers is back up under that bathroom window. (01:15:50)
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.