This is a known issue with the vSphere Client caching data for the Export List and occurs only in large environments.
If you sort the list of virtual machines by name and then perform the export, you see that the virtual machine name is populated, but all other data in the row appear empty.
To work around this issue in the vSphere Client, get all the data exported. To do this, you must scroll (with a mouse scroll wheel) or use the Page Down key through the list of virtual machines, so that the data is cached correctly and then export the data.
Note: This issue is not seen in the vSphere Web Client.