As you may know, Alistair Cockburn and Jim Highsmith organised the Snowbird retreat where the agile manifesto was developed in 2001. I asked Alistair about the lean roots of agile in an agile master class in Melbourne in 2014. He told me that he didn't know much about Lean and it wasn't discussed at all amongst the group of people who developed the agile manifesto.

Jeff Sutherland credits the idea for Scrum to the paper the “New New Product Development Flow” that came out of a study of how Japanese automakers designed high-quality new cars quickly. But this paper barely mentions Lean and Scrum didn't mention it until recently.

Also, Toyota used a waterfall production system to develop software until very recently and are still on the journey to agile. The Lean people in Japan seemed to have completely failed to transfer Lean concepts from the physical world to the world of knowledge work.

Mary and Tom Poppendeick were the first people to have a foot in both communities and to figure out how to translate Lean Concepts into Agile. They had a lot of influence on the agile alliance and the community through their series of Lean Software Development books from 2003 but they were not involved in developing the agile manifesto.

I do agree with you that there are many overlapping and common ideas in Lean and Agile but it is clear that the Agile community independently developed those ideas to solve similar problems in the knowledge worker domain.

Since 2003 the vibrant and expanding agile community embraced ideas from Lean, Servant Leadership, Knowledge Management, the US Military (OODA & VUCA) the start up community and other areas. So now there are quite a lot of agile people who have a good understanding of Lean.

But I don't see Lean embracing the ideas of agile in the same way. The Lean community seems extremely conservative and set in their ways. they seem to have stopped learning long ago.