Because the co-commentators have a big say on how an incident is perceived. They give opinion, while the main commentator gives facts, and descriptive visualisations.
The opinion of the co-commentator can cause the refs serious issues if the weight of Public opinion is with them.
Neville and carragher absolutely know this and play up to what they (and their employers) want to see highlighted.
A classic example of this is the Mane assault on Ederson. Neville said "the game has gone" when Mane received a red card. He received the card, yes; but the talk afterwards, and til this day is it was not a red card.
If Neville had have said it was a blatant red and should be a long ban, this sending off would have been cast off into football history and not brought up again. But what you see is fans compering Haaland foot up challenge for the ball against Villa as in the same bracket as Mane's kung-fu kick.
So, you see. Var listening to commentary helps them feel the mood of a challenge. They also know that, especially in games involving Liverpool and Utd, any big decision going against them will be repeated, and repeated, and repeated on sky channels and in the press. They absolutely do not want bad press.
Remember the Aguero retrospective ban for a high elbow against a team (West Ham?) at the business end of the league season? Purely down to media intervention.
If you believe the media, the TV companies, the Premier league, and the red top teams don't circle wank each other, then you are surely deluded.