With the addition of the CMake build, the IDE version-specific solution and project files are no longer required. The CMake tool can generate configurations for all supported Visual Studio versions. The last supported version was VC11 (VS2012), so right now these project files are missing support for VS 2013, 2015, 2017 and 2019, i.e. all the most recent ones.
Rather than manually copying and maintaining project files which are impossible to test, the CMake build should replace these entirely. This was the primary reason for adding it.