This is a graph of how much people spend to watch each movie. If it was a graph of how Hollywood relies on sequels, it should show how much money they spent per movie.
All this shows is that people are spending their money on sequels. If people want that to change, they should spend their money on originals.
The implication is whether it's a standalone story or not.
As example, Alien 3 is certainly a sequel to Aliens, because at the end of Aliens the story wraps up nicely and is "finished" - we don't need more.
Dune 2 is more of a continuation of Dune, however because it's the next part of the same unfinished story.
The important part from the planning and development perspectives is that Avengers, Dune, and Lord of the Rings etc were always written to be several parts from the beginning.
Its the difference between "That movie made loads of money, let's make another one" and "This story is really long, we need to do it in three parts"