In the original document, all text is under the "Normal" style. However, the "Normal" style in the original document is different from the "Normal" style defined in the new document (which, by the way, is an empty document).

In addition, the original document includes character-level formatting that is not defined within the style itself. These individual formatting changes are also being lost during the import.

Another interesting detail is that footnotes do retain their original font from the source document. However, if I copy and paste the text using "Keep Source Formatting," the text is imported correctly, except for the footnotes, which get their font changed.