Floating shelves look fragile to the naked eye because of the way they sit on the wall. All the workings of the brackets are hidden so it seems as though they are floating there on the wall. In reality they are usually much stronger than other types of shelves which are supported with traditional brackets and screws.
With standing structures, there is much more room for uniqueness. They have a large base upon which there is plenty of room to decorate. They also leave room on tabletops so that the decorator has more surfaces to work with for picture frames and trinkets. There is also not the burden of worrying if a table is sturdy enough to support the decoration.