Why is it that, after deleting a move in Chess Openings Wizard, the positions and moves after the deleted move still exist?
It’s because the data is based on positions rather than moves. Here is an example:
Suppose you have an ebook on the French defense with moves like 1.e4 e6 2.d4 d5 3.e5.
Then you add this line which starts with the queen pawn but transposes to the French: 1.d4 d5 2.e4?! e6.
Later you decide to delete the move 1.d4 because you will never play it.
If that resulted in deleting every position beyond 1.d4 then it would wipe out your entire French ebook after move 2.