Economics, and mail order.
Face it, there are less carbed vehicles on the road every day. Much of the aftermarket carb business is done via mail order, and for a supplier, Summit and Jegs are not the easiest people to do business with.
They also earned a bad rep with a lot of racers. When I researched fuel systems and carbs for my project I found warning after warning about BGs lack of quality and worst of all, poor customer service. It's one thing to occasionally let a bad product out the door. It's another thing to treat the customer like crap before you make things right.