Yes, and Anne's situation is completely different as titles are passed on in male-line. So, Mark and Anne were very consistent in their decision: no title for Mark and therefore no titles for Peter and Zara.
Harry and Meghan are inconsistent: please give us a ducal, earl and baron title; in turn we will make it known that our children should NOT be addressed as children of a duke.
I suppose it's possible they really didn't want a ducal or any title and simply went along with the Queen's wishes.