This is an interesting point.
Often guys are like "i go to sexworkers because i want that rough PSE and wanna do crazy things to her that i don't even dare to suggest to my girlfriend because she likes only soft, romantic sex" which sounds really scary, but then you ask what they mean and they say something like "cumming on face" or a bit of spanking.
Most shops/escorts wouldn't allow very rough play anyway because the girls have to see more guys than only you so their body has to be in good condition. So except if it's in a thirth world country maybe, the sex wouldn't be that kinky, abnormal or scary.
Another thing that's more understandable is if the men likes to be dominated and receive anal or something and doesn't dare to ask his girlfriend.
I can't imagine a relationship being not open enough to discuss any possible kinks you wanna try in the bedroom.
Unless it's children, animals or something very bloody and painful i would never judge my partner for asking and because i trust them i would be willing to try out most things (more than with my clients).
From what I've seen in the swinger world, it's very obvious that many "normal"/"regular" couples don't fully speak about their sexual fantasies, kinks, etc.... Often the woman is trying to pretend to be virtuous or proper, or the guy thinks his wife/girlfriend is too proper to do anything he has in mind. It appears a lot of it is social pressure, repressed sexuality, and insecurity...
In talking to a lot of guys. Often the guy might suggest trying something different and the wife/girlfriends says "no". Even threaten the guy to leave or break the relationship if he asks again. Anal sex or swinging/orgies is a major example of such requests among couples, but it can be many other things. The guys are then faced with repressing their sexual urges to keep her, splitting up with her (and lose his viable sex option or his love), or he cheats and does things behind her back.
Though it's not always the woman as culprit. It can be the woman wants to try something different, but she is too afraid to ask the boyfriend/husband and worried about what he might think of her and lose him (particularly money or security), so she represses her desires or goes cheating with other guys where she can do what she wants.
Too many couples are trying to maintain a certain false image to each other. And many are doing all kinds of sexual things behind each other's back. Cheating, prostitues, wild sex, kink, anal, bi-sexuality, swinging, watching porn (but not with each other), etc...