Because pivot ball have a different the suspension geometry with C-hub/Camber design. At the same time C-hub/Camber design has a proven performance and most of the brands have more then 10 year experience (stock) in develop C-hub/Camber suspension. It is high risk for them to develop a car using pivot ball front suspension but still has the enough ability to win in the market.
If you look at the current suspension design, the lower and upper mounting of the C-hub with A-arm and camber-link is not a vertical line. This affects the rate of change of camber in suspension travel. It also allow the A-arm to have longest extend toward outside which increase the grip and stability (Details on this kind of suspension geometry should reference to Kyosho's 1st generation Lazer buggy)