When you cantilever like that the static and dynamic stresses are multiplied the further out you extend. Think of it like a see-saw.
There comes a point where going any further requires larger and/or more structural beams and foundational support for the whole system. That effects a lot of things and will cost a lot of money so you hit a kind of breaking point where going any further becomes a major multiplier. Twenty feet of roof cantilever might cost you X but adding just one more foot to 10 more feet might cost you 2.0X.





Quote