I believe this topic has been discussed before, but I can't find it through the search function. As far as history is concerned this situation is untrue, so I can only assume it's for game-play reasons, to make the Timurids disintegrate faster, perhaps. However, there is already a scripted event that increases unrest in Persian cores. So I can't understand why this historical fantasy still exists after so many iterations. Any ideas?
Its not a problem with Persia going Shia per say, it's a problem with Persia
even appearing. Persia currently gets most of its unique events oriented towards conversion and the Shiite faith, which mean that even if there is a Sunni Persia, it will convert to Shia relatively fast. The two most notable of these events fire early in the game, with one choosing between flipping to Shia or a Stability (AI weight 100% on Shia), and the other offering a +2% missionary strength boost for the rest of the game, or a couple other benefits. Similarly as stated, Persia's size usually means that they rival the Ottomans and a historical rivalry emerges in the region.
The problem lies however with the 1444 startdate. Historically, Aq Qoiunlu conquered Qara through luck and tactical genius, then proceded to conquer Persia. After several rebellions, he lost Persia to the Safavids. This NEVER can happen in eu4. Even if Qara conquers Persia, their culture is Azerbaijani, which means a auto-acceptance of Persian. (not to mention shia state religion) The most frequent way that Persia emerges in eu4 is through Timurid rebels, specifically ones that spawn in the first 10 years. These rebels spawn even though Timur accepts Persian because
the Shia intolerance penalties are too large to overcome. Making Persia Sunni guarantees that the rebels will never spawn and Timurs empire will never collapse.