Although I have never met you, or heard of you before this post, I believe you have been hard done by, just as you describe.
The greatest shame perhaps about your exclusion from your children, as with my exclusion from my daughter, is that the parents so affected cannot be welded into an effective organisation to fight for parental rights - at least not from my experience of campaigning.
Those who have seen to it that you get no contact with your children - such as your ex. wife/partner, and all those who supported her, including the courts, see you as a piece of meat in my view, and will treat you ruthlessly therefore.
All I read on forums across the world, tells me that the laws are designed by people who think all parents are basicaaly liars, and cannot be trusted. The laws they create are so complex they are bound to fail if only for that reason - by the time you've gone through the process you've forgotten why it was you started.
I do not hold out much hope for change therefore, that will stop more "Dads" like yourself posting on this forum next Christmas, in exactly the same fashion. If it could happen to me, and to a good man like yourself, then many more will have to suffer the same fate too, especially if they do not have our strengths as parents.
The answer to your question though, is that you were excluded because your courts believe they know better than you do what is best for your children, and are compelled to base their judgements on that bogus concept (almost regardless of how good a dad you've been).
I hope that satisfies your need for an explanation.
All the best, Graham