Java was propelled by investment banks that saw Java as a manna from heaven comparing to C++ CORBA and the mess it was. Suddenly you had something simple yet even more powerful than C++ when it came to time to deliver a flawless distributed app. Java's main drawback is the amount of boilerplate code, but frankly that's more of an issue of framework/design patterns than the language itself; similar problems are in Python, Scala or even Haskell, just at a slightly higher conceptual level.

Language-wise C# overtook Java quickly, but SUN was all about openness and about not being big bad Microsoft, and that resonated with the majority of idealistic developers.