.NET is primarily used by two cultures that don't place a big emphasis on open source development: Windows and giant in-house enterprise IT projects, often at b

.NET is primarily used by two cultures that don't place a big emphasis on open source development: Windows and giant in-house enterprise IT projects, often at banks. Banks have historically struggled with open source: it took a long time for them to start using it, and much longer still to start contributing. Java's focus on cross-platform support from the start probably seemed like a waste of resources back in the 1990s when Windows was so dominant, but it had the advantage of making it more popular amongst UNIX users and the existing open source culture. Java going open source long before .NET also contributed to this. The end result is that you get organisations like Red Hat, Apache, IBM that create vast quantities of high quality open source Java code, and a culture that is steeped in open source development. Whereas in .NET it's rare to use components not built by Microsoft and when they do exist they are typically proprietary, same as in the 1990s.