When I was at GS it depended highly on which teams you were on. In FICC, where I was, SecDB/Slang ran everything, but there where definitely signs that it was falling out of favour elsewhere and more Java and C# projects were emerging.

If I were to speculate, I'd say that although GS has a large technology investment in SecDB/Slang, it's still a language that was invented a long long time ago by technology standards (I don't know exactly when it emerged, but I'd say it's safely a good two decades or more old), and it just doesn't have the performance or features that new languages have with current generation compiler and JIT techniques.