a lot of married women are bored in their relationships.
This is true. It's not only married women. Women in long term, non-marital LTRs tend to get bored somewhere between 2-5 years. It's closer to 2-3 if the guy exhibits more beta tendencies. Men who retain stronger frames as a relationship progresses can keep her less bored for closer to 5 years. Men also tend to become more beta as relationships continue.
The majority of my local friends are men who have been with their same girlfriends (in most cases, now wives) for 5+ years.
Long term established couples do a good job of hiding their problems from the outside world. If you're good enough friends with a man in an LTR/married man, he'll tell you about how less exciting his relationship is now as compared to the first 2-3 years of it.
A woman in a long term relationship is much less likely to inform a random man about her boredom in it. This is the real life application of what I said above about hiding problems. As a result, it becomes more difficult to find a woman in a longer term relationship who is open to extramarital/extrarelational sex.
