Hello @Chaoyue and welcome to Microsoft Q&A. Please allow me to explain what I know related to this issue. This starts with elaborating on the difference a Hierarchical Namespace makes.
BLOB storage and Data Lake Gen 2 are very similar. Data Lake Gen 2 is the result of enabling the hierarchical namespace feature on the storage account. The effect is to enhance the blob storage so that folders are no longer virtual, but actually have an entry. The entry, when viewed via blob driver, presents as an empty blob.
An empty blob can be created when you try to use a Data Lake Gen 2 driver to write to blob storage (without hierarchical namespace). In an attempt to make the new folder, this empty blob is created.
To better visualize, imagine a filing cabinet. The filing cabinet is your storage account. The drawers are the containers.
Without heirarchical namespace (blob storage), you are placing papers directly into the drawer. The papers might be sorted and have parts of their names declaring some papers belonging together , but they are still loose.
With heirarchical namespace (data lake gen 2), you are placing file folders in the drawer, and placing papers inside those file folders.
Remember, file folders are also made of paper just like your documents, so if you ask "show me all the things made of paper in the drawer", you will get the folders too. However the folders don't contain any data, so they appear empty.
If you try to insert the file folder to the first case, it will appear beside the other document papers, but hold nothing inside.
Does this make sense? Or have I missed the mark?