So, personally for us I think the whys were very important. My H never for an instant tried to blame me or the M, and we actually had what both of us considered a good and happy M. So it was especially confusing for me.
My H wrote me a pages long narrative at 5 months out about all the things that led to his faulty boundaries, attachment, etc. Believe me there was plenty of FOO, CSA, etc, but he also included boundaries, self-esteem, selfishness, ego-boosting, depression, opportunity, work stress, etc. For him he believes it was a "perfect storm".
And yes, it did help me. A lot. I actually read that narrative regularly. He owned it all, apologized profusely, discussed how much shame, revulsion, etc he now feels and how grateful he is that I have given him another chance.
And he has continued to grow since then. And changed so much. I actually feel safer with him now then I did prior to either Dday. I feel like he is "mine" in a way that I never did before; that he feels connected to me and puts my needs and interests equal to his own. That we are a team and have each other's backs.
I don't think either of us would be where we are without the hard work he put in to discover his "whys".