ExportProjectContent in PowerShell outputting JSON not MPP files when trying to export P4W files

We are trying to figure out how to export MPP (project) files from project for the web. Using the following instructions from Microsoft (https://learn.microsoft.com/en-us/project-for-the-web/export-user-data-from-project-for-the-web), I performed an export using PowerShell, but was given JSON files as an output, as opposed to MPP and XML files as stated by Microsoft. Does anyone have any ideas on what's going on here and how I can get to the MPP files? Thanks!