1) The OP is asking why he's getting an error trying to access "members _11 _21 _31" etc. I have correctly answered why this is occurring. You have not.
2) While I do assume OP is using Visual Studio as we are dealing with the DirectX Math library here the advice of "going to the definition" of XMMATRIX is sound and teaches the OP how to get to the root of the problem.
3) I have not recommended disabling SIMD. But it appears to be the only way to access elements NAMED _11 _21 _31 if you need to do so for learning purposes.
4) There are additional ways to access the individual components of the matrix including the one you pointed out.