Maybe because the myth of Lucas’ master plan persists, when he too was making it up as he went along?
This. It’s pretty clear that the only “plan” for the prequels were a set of bullet point events/moments he more or less forgot about until Episode III and then went “Oh shit, I still have to do X and Y and Z…”
And we all know there was no overall plan for the OT as it was being made.