Why do the Nords of Western Skyrim have a German accent during the Interregnum?

Playing through the Western Skyrim DLC in ESO and was surprised to hear a lot of German-sounding accents in Solitude (the most obvious thing being all the 'ze's and 'zere's instead of 'the' and 'there'), when the Nords of Eastern Skyrim sound much as they do in TES:Skyrim (including in Solitude, I checked!) and the little Morrowind I've played (like...well...Nords).

Do we have any particular reason for the difference?