Not needing to care about win7/8 is relatively recent (a few years now, but a lot less than ten), and fully supporting both dx11 and dx12 with no caveats was sufficiently difficult that most games didn't really take full advantage of dx12 until they could drop dx11.
Not needing to care about win7/8 is relatively recent (a few years now, but a lot less than ten), and fully supporting both dx11 and dx12 with no caveats was sufficiently difficult that most games didn't really take full advantage of dx12 until they could drop dx11.