There was a similar situation before. Nzonzi fouls Dybala for what would have been his second yellow. Instead of simply falling, Dybala decided to make a pass to Ronaldo, who made a shot. The ref gave an advantage. Var wasn't used, but if it was and if the ref followed the same criteria he followed for Costa's disallowed goal, it was gonna be a red card for Nzonzi. Imo, it was correct not to use VAR since advantage was given.
It was the same here. If Matuidi won the ball and made the pass after making the foul (like Lichtsteiner did once in the past when we had a goal disallowed) then sure, use VAR and disallow the goal. But here the Roma player didn't fall and decided to go for an attacking pass (with his left foot, while being fouled on his right). He even continued running after the foul and before the pass. Advantage was clearly given and if the pass was successful, it might have been a goal for Roma.