They already are... they are recognized on the AFI top 100 and regularly come up in the conversation as among the best ever made.

These sorts of posts always annoy me as they largely either try to elevate movies that aren't that good in the first place or they proclaim films that are widely praised as being somehow underrated. A quick Google search of the films would tell you how they are viewed in the context of history though.

Take a look at any of the best of all time lists and it is likely one of the trilogy, if not the whole thing is on there.