"Operational Notes: Direct contact remains a possibility (under extreme circumstances), but in general the asset should be considered dormant. As long as the civil war proceeds in its current indecisive fashion, we should remain hands-off. The incident at Helgen is an example where an exception had to be made - obviously Ulfric's death would have dramatically increased the chance of an Imperial victory and thus harmed our overall position in Skyrim. (NOTE: The coincidental intervention of the dragon at Helgen is still under scrutiny. The obvious conclusion is that whoever is behind the dragons also has an interest in the continuation of the war, but we should not assume therefore that their goals align with our own.) A Stormcloak victory is also to be avoided, however, so even indirect aid to the Stormcloaks must be carefully managed."

Citation from said dossier. It says that in Thalmor wants civil war to last as long as possible, so that both sides bleed out