"I was not involved in One World Tree. Why did it decline?"
OWT was created by a computer program that combined parts of sundry AncestryWorldTrees. What sort of algorithms defined what was going to be copied and what not have not been disclosed. To my knowledge the composite mess was "updated" twice while the AWT software was still supported in the site back end. No non-Ancestry.com individuals could make changes in OWT. If someone screamed and hollered loudly enough about one of the bizarre cross-connections created by the program, some Ancestry.com programmer might be told to make a change.
The program created many of its own errors in addition to copying erroneous tree stuff. It will never again be 'updated'. It just sits there taking up server space, a trap for the would-be tree-copier.