No. Most women would put in a lot of effort to improve, and to teach their hubby, for a mutually satisfying sex life.
But after several years of her trying to encourage a better sex life, but perhaps still being ignored / taken for granted / feeling unloved, etc, and one day a nice man flatters her, or gives her special attention, her head may be turned and her mind may start fantasising, and then yes, she may "fall into" an affair.
The married women that Ive known who have had an affair, did so because they felt their husband was not being affectionate or loving towards them, not listening to their wife or making an effort to fulfill her needs, and so the women felt they needed something more emotionally, something their husband can't, or won't, or has stopped giving them (perhaps he's also giving it to somebody else?).
For the record, I am NOT condoning adultery. I believe all cheating is wrong, no excuses.