From the article: “A year later the missing skull fragment was found on the orders of Stalin, who remained suspicious about Hitler’s fate. “
There is the answer. Stalin ordered the skull fragment found. Not finding it would have resulted in those ordered to find it being put to death. This was Stalin after all.
My thought is that someone “produced” this skull fragment to placate Joseph Stalin.
But between the Soviet Union and Nazi Germany just imagine how difficult it would be to find a skull with a bullet hole in it.