@Geddy Lee's Fee and See (can't quote you, sorry)
I can only categorically speak for myself here, but I will.
I love my husband dearly. Very dearly. I believe, and so does he, that we have a strong marriage and a strong partnership. We've been together most of our lives. He is my rock, and he would say I am his.
But my relationship with him is qualitatively different from the one I have with, say, my mother in law (to whom I am extremely close).
To cut to the chase, I fuck him. I don't fuck anyone else. Our relationship has a dimension, a very important but also a very finely balanced dimension, that doesn't exist in those other relationships. And because it's very important for a functional marriage to keep that sexual relationship alive and functional, there are things I just don't fucking want him to know or to talk to him about. There are things you do not share with someone who you hope and expect to experience sexual desire for you.
Like, I think after five kids, I'd be happier if I had some work done on my tummy. Flatten out the folds, that sort of thing. I don't like how it looks and it affects my confidence. There is no fucking way I am going to discuss that with him. I am not going to tell him I feel unattractive, because there is no way that conversation ends well. Either he agrees with me, which I will put a hard face on but in reality will devastate my confidence and make me inwardly spiral, or he doesn't agree with me and tries to talk me out of my own opinion about myself, which will make me defensive and also secretly I won't believe him. The poor fucker can't say anything about that subject that would be 'right', so out of fairness to him I don't say anything.
We had to go to therapy (more accurately, he had to come to therapy with me) about something childhood-related. He was upset I had not disclosed this issue. I remain fundamentally enraged that due to circumstances, he had to find out, because that is not something I ever wanted my sexual partner to know about me. I love him and trust him completely. I still hate more than I can describe that that might be in his head when we are sexually intimate. I will never stop being afraid that that's what he's thinking.
There are just things that should not be shared in a sexual relationship, because they will rot it from the inside out. I know a great part of what attracts him to me is my confidence, because he's always been pretty shy. I can't afford to compromise that by telling him every fucking vulnerability and weakness and fear I have.
He's my husband. He's not my priest. The marriage bed is not a confessional. There are things you share, and there are things better left unsaid.
For all those weaknesses and fears... that's what close friends and trusted family are for. I don't need my mother in law to fancy me. I very much need my husband to do so.