Why do mothers let their husbands sexually abuse the children?

First off let me say that I'm very sorry this happened to you and that you're a very strong person being able to deal with this.Yes, I believe that your mother is supporting you now because she feels guilty for letting this happen to you. I feel its self esteem issues. She doesn't want to leave the husband because she feels she will never find love again. Those motives are selfish, but these things happen. It's good that you are not holding a grudge against her. I believe many good things will come to you with the attitude that you have.