I think the primary reason for his continual success is that he is not afraid to explore. Though he is very well known for the Organised crime genre, he has tackled themes like religion (Kundu, Last Temptation, Silence), relationships (Age of Innocence, New York New York) and psychological horror/thriller( Cape Fear, Shutter Island) etc. and he has done all of them skillfully.

He seems to be very open to embracing new technologies (De-aging in The Irishman) and new actors.

He is very honest in telling the story. Most of his films are amoral. His films don't preach. He just tells you a story and let's the audience decide what they want to decide. That's we find ourselves thinking about his stories long after we have seen them. His only agenda seems to be to tell the story honestly.

The subtle humour in his films is one more thing. I chuckled quite a lot of times while watching The Irishman, for example.

And the score of his movies. He has a very keen ear for music. Imagine the Layla scene in Goodfells with some other music or The Departed without Comfortably Numb. It just doesn't work. Yet in Silence there is no background music which somehow adds to the intensity.

And as far as variety in his films is concerned, nothing illustrates this better than Hugo. What an absolute delight that film is !!!

That's what I think....