The short answer is because of VAR.
WORLD CUP linesmen have been told NOT to flag for offside during the tournament - here’s why.
www.express.co.uk
But you might also be thinking of the "delay" that had already been instituted before VAR. Several years ago it was decided that the AR shouldn't raise his flag until the player in offside position either touches the ball or interferes with the opponent.
By Randy Vogt I was an assistant referee and yellow was up 1-0 in the closing seconds of a Boys High School Summer League semifinal game. A maroon attacker was at the top of thepenalty arc and he played the ball to a teammate a half-yard offside on my near side of the field, inside […]
www.socceramerica.com
Law 11 on offside is soccer’s only complex rule and it has become more complicated of late as the AR must delay raising the flag as many things could occur before the attacker in an offside position becomes involved in the play. He becomes involved by interfering with play (touching the ball), or interfering with an opponent (such as challenging for the ball with a defender right there or being in the visual path of the goalkeeper when a shot is taken), or gaining an advantage (the attacker is in an offside position when a teammate takes a shot and the ball rebounds off the crossbar or upright to that attacker or comes to the attacker from a deliberate save). The only time with the offside decision that the flag should be raised quickly is if the attacker in an offside position could collide with the opposing team’s keeper.
