The real problem with football we are asking the video ref to judge on things like fouls which in the rules of the game is a matter of the opinion of the ref. Two people can watch the same footage and come to 2 different conclusions.

The problem with offside you need a camera dead in line with the offence. For it to work effectively you're going to need cameras all down the touch line.

In other sports sports video refs are asked to judge on fact. Like a run out or foot in touch or was the ball grounded or did the ball go forward, etc.

In cricket technology has allowed them to create a virtual reality in ball tracking for LBWs and snicko to see if its hit the bat. They make the decision totally on the outcome of the technology. Like if there is a spike on snicko it is assumed to have hit the bat. Its not a question of opinion of the third umpire.