Hi Jane
The area where a Jones fracture happens on the bone where there is not a great blood supply. The poorer blood supply does mean that a failed union of the bone is a frequent complication
Did you go into a cast first off then it failed to heal and the surgeon subequently operated or did the surgeon operate from the start?
If it was the former the aim of the ORIF is to bring the bone ends close together so that the fracture is more likely to heal. With the bone ends closer together the bone building cells (osteoclasts) have less work to do and it is hoped this will improve matters. So compression should be a good thing.
If the surgeon did the surgery did this at the beginning it may have been indicated for lifestyle factors (eg you are an athlete) or the nature of the break.
The ORIF is unlikely to be a cause of non union.