After reading most of the threads about this topic and the different theories. I think the reason wives won't have sex can be summed up in four words. They don't WANT to!
Basically we as humans do what we WANT to do!
There are various motivations for wanting to do something, but it basically comes down to two things. Either we want to do something because it provides a BENEFIT or we we want to do something so that we don't have to receive a CONSEQUENCE for not doing it.
The theories that are floating around on this site about how to get the wife to be more cooperative are basically saying the same thing. They are telling the husband he either needs to provide a benefit strong enough to make her want to have sex or give her a consequence strong enough for not doing it that will make her want to do it instead of receiving the consequence.
If the wife can not be motivated to WANT to have sex then the husband has to make some choices - accept things as they are and deal with it (in whatever manner he can) or get out of the marriage.
It is really quite simple in theory. Not so easy in practice.
I am ashamed to say I was a wife who, for over 25 years, more often then not denied sex to my husband. I had excuse after excuse, but the bottom line was, I just did not want to have sex with him. Pleasing him and providing him pleasure, orgasms, or other benefits were just not strong enough to make me want to do it. And, I was more willing to accept the consequences of having a distant, angry husband then to have sex with him.
I see things differently now! I have come to realize the benefits of having a happy healthy sex life - both for me and my husband physically and emotionally. And I no longer deal with the consequences of a distant, angry husband. Our marriage is still far from perfect, but oh so so much better. In fact it is so good in many ways. Hind site allows me to see the pain and anguish I caused my husband, not to mention the pleasure I could have had if I had only allowed myself to let go and feel it.
So many wasted years and so many regrets! But, thankfully, years ahead to make up for it!