Wet dreams are good or bad? Why only few men would have wet dreams and few men does't have for the whole life.

Neither. Wet dreams are neither good nor bad. They just are what they are. Why do some people have more than others? No one really knows. On average, they tend to decrease with age. Hope this helps!
Normal. Wet dreams are a normal occurrence in a male ,especially, after puberty. This is healthy and unfortunately will eventually disappear with age.