This is a user error. To get a copy of the metadata display that is available in ArcGIS Pro, save the file using the Save As option instead of exporting it.
The metadata display in ArcGIS Pro is an HTML representation of the item's ArcGIS metadata. The information in this issue is related to a copy of the HTML display used within ArcGIS Pro. This workflow is described in the first bullet point in the help topic Save a copy of an item's metadata, which involves saving a copy of the item's ArcGIS metadata to an HTML file. Refer to the following documentation:
https://pro.arcgis.com/en/pro-app/help/metadata/save-a-copy-of-an-item-s-metadata.htm.
Exporting metadata is the process by which an item's ArcGIS metadata (displayed and editable in ArcGIS Pro) is converted to an XML format that is specified by a metadata standard. This is described in the help topic, Export metadata to a standard format. Refer to the following documentation:
https://pro.arcgis.com/en/pro-app/help/metadata/export-metadata-to-a-standard-format.htm.
The exported files in this issue have the correct output for the options that are selected according to the content of the ArcGIS metadata describing the model. This is the expected behavior, and the software is working correctly. Metadata standards are not well suited to documenting geoprocessing model parameters. This information cannot be put in a standard-format metadata document, which is why this information is not included in the files generated by the export process.
The default Item Description metadata style is used to provide metadata, and a different metadata style must be selected to provide additional metadata content that supports the requirements of the metadata standards. A lot of additional content could be provided to describe the model if another metadata style is selected. If the additional information is provided, the content would be included in the exported XML files.