Hey Haident,
Although the Activities screen and the Work Order screen are both based off of the Activities table, the Outlook plug-in is not meant to support Field Services.
The Plug-in was meant to sync your Activities over to Outlook, a Work Order is not the same as a scheduled activity. Although, you may be able to configure the Outlook Plug-in to sync your Work Orders, but this will affect the way your normal activities sync as well.
In a later version of the plug-in we may add support for the Field Services Module.