The list of file formats that CAD users need to deal with never seems to stop growing. For a long time the ESRI Shapefile was pretty much the exclusive format from ESRI users but it was always an export from the GIS. Now users find themselves receiving folders of content with the folder having a .GDB (GeoDatabase) extension.
ESRI Shapefiles are not just the SHP file. While some importers can import the geometry from just that one file, a lot remains missing. That’s why it’s important to send the package, not just a single SHP file.