Smoking Weed being so common ?

I am 19 years old and never smoked weed and i'm proud of it. 95% of my school did it so i feel more accomplished...what doesn't make sense to me is how common it is nd how soooo many of my friends tried to talk me into it when all i see it did to most people was turned them into stone heads that even when there sober they act high becasue there brains are so turned to mush already. i'm not knocking anyone who smokes weed here and there its just not me and i have no reason or interest to ever take it...but why soo common ?