In Confluence, when the user inserts an Excel file directly into the page, the same will display the content on the preview/thumbnail, but, will lose original attributes from Excel, like the tables, making the content to be similar to a simple text file.

As a workaround, while the users can use the Excel macro, since the preview is used for such functions, the same should display the file as it is in Excel. This is a suggestion to improve the Excel preview, keeping its original attributes.