“Please tell me why my husband can’t talk to his parents even about the most little things like saying happy birthday to them or inviting them over for a meal. I have to do it all. I make all the plans for everything and he just fits in. I am so tired of being the center of all the plans for everyone and when things go wrong I am blamed when someone in the family could help. We have been married almost 20 years.” (Letter shortened)
I cannot tell you why your husband is the way he is, and I doubt it would be something he himself could articulate, even if he himself did know. In the unlikely event you did reach a convincing diagnosis about why he is the way he is I am not sure you’d have anything useful or helpful. [Gaining understanding or insight does not necessarily lead to change in behavior.]
What I do know is that while your husband has a spokesperson in his wife (and life) there is little reason for him to see the need to have a voice of his own. People tend to fall into roles that most suit them, and I doubt very much that you’d find it very easy if your husband did begin to direct the family traffic.