This may be a controversial answer but my opinion, in a nutshell, is because of business decisions that prevented or discouraged it from being supported by plat

This may be a controversial answer but my opinion, in a nutshell, is because of business decisions that prevented or discouraged it from being supported by platforms beyond Microsoft's. As a developer I had no interest in tying myself down to a technology that didn't work on all the devices my users loved. There was some effort to port it to Linux, but it was too little, too late. We really needed Microsoft to not only release the whole shebang into the wild, but make it attractive for Mozilla, Apple, eventually Google, and the whole ecosystem to adopt. Flash was dying and there was a great opportunity give the world a platform to enable more rich web applications than were possible on the standards-based frameworks of the time. Thankfully WebAssembly does not repeat this mistake.