the same reason why goal line technology was only recently introduce in the world cup ( corrupt seb bladder the dinosaur)
I propose you do away with human eye for the offsides and concentrate on the activity areas so the lines men dont run up and down but focus on what is happening. After all the computerised analysis of off side looks remarkably like hawkeye in tennis.
Maybe the refs can carry a screen like the size of the mobile phone on his arm to check replays or video sent by the tmo. Heck why not use thermal imaging to show hotspots when contact is made so divers cant just kick the ground?
People talk about the flow of football but each time a foul occurs it pretty much stops the play for enough time to get a replay. I mean so far there been so much diving and playacting you could fill an episode of Eastenders and cast Robben as Phil mitchell? 🙂