Rehab may not be the best way for him to stop drinking. It might be weird to hear or understand but people are different. He may be better off seeing some type or therapist or trying other methods to quit drinking on his own.
It also stems from the very simple fact that you can't help someone that doesn't want to help themselves. If he's giving up that's going to be hard to understand. I know people who have done 10 20 even 30 stints in rehab programs. Some give up some never do and thankfully some get better.