All the married women I've seen appear to be very happy.
Appear - that doesn't mean they are. You don't have to spend long looking at threads here to know many women are not happy in their marriages, and some women do consider starting relationships with other men.
None of the above could ever be true if a large proportion of men were abusive. If that was the case, almost all women would choose not to have any romantic relationships with men.
But abusive men can be charming and charismatic, particularly in public and in new relationships. If they were always obviously abusive, then probably they wouldn't get into relationships. Plus for a whole host of reasons, some women are poor at spotting red flags, may have low self esteem, or already be trapped by children, finances, work, housing.
Two women a werk are murdered by partners - some of those men may be repeat offenders who weren't previously caught, but even if that's true, it would be logical to assume that many more women are being abused without being murdered - partly because there are stats, but also because people are unlikely to go from always nice to murder in one step - it's behaviour that escalates, and there will be a lot who are physically abusive but don't actually kill. Plus there will be a lot who are coercive controllers without being physically abusive.
And you won't see it most of the time. Women won't go out, or they'll wear make-up and clothing that conceals injuries. You won't get to talk to the women who will get a beating back home if they talk to other men. Nearly everyone is socially trained from childhood to say they're fine, their relationship is fine, except to closest friends and family, and some won't say things aren't good even then.