Open Asset Properties panel, notice that other properties can be modified but not created date as its disabled.
Now this created date proprerty gets added when assets is created in AEM and remains as it forever.
Now check /libs/dam/gui/coral/components/admin/contentrenderer/base/init/assetBase.jsp
where assetLastModification value is set as created date. Means its degined in such a way that last modified and created date remains same. Hence it never gets updated when any property is modified also.