Here are some situations that would cause them to tolerate it.

(a) They are not financially independent and therefore have no choice, for many of them depend on their husbands even for their next meal.
(b) They are not aware of the laws that deal with the problem.
(c) They worry about how they would bring up their kids without the help and support of the husband.
(d) In some cases, the woman may be educated and employed, but has got so used to the luxuries available from her marriage (like a holiday abroad, a car, and so on) that she may find it difficult to do without them.
(e) In Indian society it’s difficult to settle down separately as people look down on such women, unless she is rich, or a celebrity.

Some tips
Here are some tips for married women in distressful situations.
(1) Become financially independent. And this is not just to be able to cope up with a situation of wife beating, but to prepare for such uncertainties as premature death, and so on.
(2) Educate yourself about the law by talking to a lawyer friend.
(3) If you are worrying about the future of the kids, you must first realize that living in such a disturbed environment would affect them more than if you were living separately.
(4) Be practical, while taking the decision, and don’t let your decision be influenced by luxuries.
(5) Do not care about what the world might say. It’s your life that’s at stake and only you should be responsible for your decisions. This ‘doesn’t-look-good-in-front-of-the-world’ thing has made many to suffer.