As someone interested in marriage, I find it interesting to read about people's problems in marriage. One common problem that people complain about is sex (or rather the lack of sex). But honestly, barring unusual circumstances, having problems with sex is just a manifestation of problems with the relationship.
I know people frequently say things like their sex drives are mismatched, or they are too busy, but this is just frippery. Sex hardly ever takes longer than half an hour, especially once you've been married a while and know just what to do. Since the average American spends 4 hours a day watching TV, being too busy is hardly the problem. I agree that people can have very different sex drives, but this just means how often you, unprompted, feel like having sex. It has nothing to do with how often you can actually enjoy having sex.
An example: In normal circumstances (no one is very stressed/ill/etc.), B likes to have sex every day or every other day. In an unprompted state (ie B is not here), I want to have sex maybe 2-3 times/month. Otherwise, I don't really think of it at all. Nevertheless, we have sex 3-4 times/week, and I enjoy it very much almost every single time. This is because 1. B is very sexually considerate and 2. I like him so I like to give him pleasure and connect with him in a sexual way. If I really don't feel like I can have penetrative sex for some reason, then I give him a blow job or hand job or something like that. It is enjoyable to please him. Actually, it's a lot like B always cooking for me: he likes cooking for itself; he likes cooking for me because it pleases me; it's a way for him to show his love for me; and then we get to eat a nice meal together.
Interestingly, when B is very angry at me, he doesn't like cooking for me. He would either refuse to cook for me or would cook, but only begrudgingly, in a way that ruined it for me. We have never gone for more than a few days continuously angry at each other, but I can imagine that such a situation could easily persist for longer. He might do this to punish me or extort concessions from me, but more likely would just not feel like it due to deep-seated unhappiness and anger at me, which he may not even be fully aware of. I think that the people (usually men) who complain about sexless marriages are usually in this situation.
By this I don't mean that the one wanting sex did something really bad to the one not wanting sex, or at least not usually. I think it's more that in every relationship, both people have scorecards and give each other points or demerits for various behaviors. These points or demerits are individualized and amoral. For example, B can get points by being affectionate; telling me my behavior is ridiculous; and hanging out with my family. He does not get points for letting me decide things, even though I like this; for picking up after himself; or for financially supporting me. He gets demerits for not listening to me properly; being sad; and accidentally making noise in the morning. He does not get demerits for never buying me gifts unprompted; being cheap; and never doing housework.
So when people give advice to those in sexless marriages like "You need to help around the house more", I think they are fundamentally wrong (in B's case, this would earn no points and so would not affect my feelings towards him). Rather, the sexless one needs to figure out 1. what actions earn points and demerits and 2. make sure that they always have more points than demerits (although I think twice as many is a safer goal for avoiding problems). If you have more demerits than points, your spouse will feel deep-seated resentment towards you. And if you do not act quickly to correct your demerit/point imbalance, the resentment will continue indefinitely (and thus they will no longer want to have sex with you). Having more points than demerits is especially important since most people are irritating. Extra points lubricate everything so that you can happily ignore the more frustrating aspects of your partner: otherwise, everything they do is constantly grating at you.
The men in sexless marriages who say "But I make a good salary/help around the house/am in shape" are therefore demonstrating a fundamental cluelessness about the very important point system (since it is individualized and amoral). They need to figure out what their wives award/deduct points for and act accordingly. (This goes for women too, of course.) If they can do this, they will have as much sex as they want.