Would you expect an aircraft to use all the length of the take off run available for its ground run and why?
No reason why a takeoff can't be TOR limited. However, keep in mind that this doesn't mean that the wheels are on the ground until the end of the TOR. Although there are different standards in play, the usual requirement is that half of the air distance to screen height has to be over the TORA .. ie the aircraft has to be airborne this distance prior to the end of the TORA.