I know it doesn't make sense , but for the sake of the team you can't have two brilliant drivers. The wheels come off and it tears the team apart from too much rivalry. Many teams have suffered from this in the past and it effects the teams performances in the end. Senna and Prost was a prime example. They won 15 out of 16 races in the season and dominated yet they were fighting each other. Prost left and the team fell apart.