What are the ages of you and wife, and how long have you been M? How many kids and their ages?
Age, health, and the daily stress of family life can all affect how much or little sex the couple has, and that's not counting outside sources of stress. Does your wife have a full time job outside of the home?
It sounds to me like your W has an unhealthy mental attitude. Therefore, she is unhappy......and that affects everything and everyone in the family. It can affect a person's sex drive.
Growing up in a family of negative attitudes can certainly influence the children. If one of the parents were whiners, complainers, fault finders, perfectionist, they think everyone is out to rip them off, etc. and etc., it can certainly "rub off" on their offsprings. If her parents yelled and screamed in her childhood home, she probably fell into that same model that she observed growing up. We often mimic our parents, and don't see it in ourselves, but others can see it.
I believe a lot of those type of negative attitudes can be changed, if the individual wants to change. Sometimes, being educated on the topic is enough to guide the person in a new and better direction. Other times, it may take therapy, life coaching, or spiritual guidance to overcome these nasty outlooks on life. However, the key is willingness. She has to be smart enough to know she is making her life worse....and life for those around her worse, by this terrible attitude.
I can see how it could wear you out, living with a person who never sees any good in anything.
When the two of you were in counseling, I take it was for the MR? Did the counselors address her attitude?
Has the subject of divorce been discussed? Has your W said she wants a divorce?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!