[orthoxerox]

Unity and XNA, but mostly Unity.

Unity used Xamarin to target iOS and Android, so this meant using C#. As Unity's popularity grew, so did the use of C# in gamedev.

XNA was a very well-designed game framework (not engine) that allowed many people to get into indie gamedev without learning C/C++ and SDL or OpenGL. Java had nothing comparable, libGDX was released only in 2014. If you followed one of the indie stars and tried to emulate them, you were quite likely to learn XNA or one of its reimplementations.