The reason, from my understanding, is that she does not have the emotions that she needs nor the desire to do it. Perhaps her love bank is empty as I will elude to in more detail in the following post.
1) I feel that perhaps she is still in withdrawal from the ending of her affair. I.e. not fully ready for the piecing that we need to do.
2) Perhaps her hormones have shifted after her 3rd child. (which I desperately hope will shift back.)

I do not believe that it is due to my competence in the bed as she seems to be capable of fulfillment as I discussed in my prior post. It is definitely a desire issue.