Why do most married women deny to their husband that they enjoy having sex more with a well-hung guys.

For the same reason they don't discuss many of their desires, they are culturally shaped to a certain mindset and have trouble thinking about what they really enjoy much less talk about it especially with their partner. Communication is key especially if you are in or considering a lifestyle that has her with a sex partner other than her spouse. Your brain can process a lot more than you think if you allow yourself to hear things that in a conventional mindset challenges your masculinity. A non conventional lifestyle requires a non conventional mindset and communication.
 
I may be repeating what others have said but my wife prefers men with average size cocks who know how to please a woman. She's had bad experiences with guys with large cocks because they just plowed into her with little or no foreplay.
That's got nothing to do with her liking or disliking big cock, it only has to do with her not liking the way those guys mistreated her
 
Yea my wife was like pry teeth out to even tell me she had a bigger cock a long time ago. I told her I’m ok it’s not going to hurt me I just think it’s hot if you have and she finally told me her ex was bigger. Then I found out about when her ex and her where having issues she was bang the super fit neighbor while he was working. I asked her was it once or multiple times cause that’s hot and she plays that I don’t remember or I don’t recall card
more than just once I would guess
 
Wife says size can matter if you know how to use it concerning penetration, rhythm, and pussy and hip signals. She says some big guys just barge into her pussy and bang away like it's only size that is the answer. She says that sometimes a hard banging just makes her numb. I'm not large but I please her because I know the angles to bust her with and signs of her wanting to be slow fucked from the head barely in to slow penetration fully shaft. I think experience matters more than size.
some lover with small or average sized dicks can also be poor lovers as well as well-hung guys