Because, we want to believe that the old "before alcohol" person is still there somewhere, underneath the disease, but it's not true.
I've spent over 8 years trying to get that person back, but he ain't coming back. I will never have the man who could make me laugh by saying one stupid line, who would willingly take his child to the park to play, to the river to fish, anything to give me a few hours by myself. Who would do anything besides sitting down and either watching tv, or playing video games. It's taken me this long to finally understand that.
You going to anger management won't work because, at least in my case, my biggest source of anger is AH. Watching him self-destruct, and bringing the rest of us down with him is a BIG trigger to my anger. Couples counseling? I wouldn't even consider it with an active alcoholic, and no way with my AH. he'd use anything I'd say about him against me during one of his drunken rants.
Unless you remove yourself from the situation, or he goes to rehab(preferably both really) then the cycle is going to continue. Alcoholism isn't just a problem for the drinker, it's a problem for everyone involved with him.