THEY JUST DID...
Seriously though. Lets look at a few of the continuity problems.
According to The Phantom Menace... This whinging bucket of bolts was created by... Anakin Skywalker, whilst he was a slave on Tatooine.
In Episode whatever: A New Hope. aka The Original; Whingebag and R2D2 escape from Princess Leia's ship to... Tatooine. Yet for some strange reason Whingy doesn't recognise his home planet.
In addition R2 meets Whingy for the first time in Mos Eisley and for some reason he doesn't recognise his surroundings upon his return, despite having a bottomless pit of a memory.