A massive library of tutorials existed for C# and XNA.

Failing Bird is a clone of the viral sensation Flappy Bird . While the original game took the mobile world by storm, this version was developed specifically for the Xbox 360. It was created using the XNA Framework, which was the backbone for the Xbox Live Indie Games (XBLIG) marketplace. The Role of JTAG/RGH Consoles

Because Microsoft eventually shut down the XBLIG marketplace and limited what could be published, the homebrew community became the only way to play many of these "lost" indie titles.

To understand why Failing Bird is significant in the indie space, you have to look at the hardware it runs on: