Why?
Because it can be a low key, fun and social activity. It can expand your mental horizons for a bit, let you see the world in a different way.
Weed isn't addictive, not physically. How do I know? Because nicotine is addictive as fuck and it is physically addictive. You know that feeling when your thirsty? The urge for water, that need (not necessary the dry throat). Welcome to every three hours when your a nicotine addict.
I did a ton of weed freshmen year of college. Came home for the summer, no withdrawal and I didn't give it a second thought.
All of this is anecdotal to you.
Say you tell someone to take up weed and he's a addictive person, and is stuck with a habit that is draining his life? What now?
You smoke? ok, but keep that shit to yourself.