Current ecosystem has NPAPI that allows anybody to integrate them with any browser, including open-source ones (within limits of platforms supported by Flash/Silverlight).

EME/CDM deliberately doesn't have such API, and thanks to DMCA browser developers without a license and proprietary SDK for each CDM are not even allowed to use the CDMs.

e.g. with EME Hollywood can say that nobody can develop a browser that plays video on a TV and legally enforce that.