Under Shia (Ithna Ashari) law, why is a talaq pronounced by a husband under compulsion ineffective?

Shia law requires the husband to pronounce talaq of his own free will and with a real intention to dissolve the marriage, so a pronouncement extracted by compulsion lacks that intention and does not take effect. Hanafi law takes the opposite view and treats a talaq under compulsion as effective. Shia law does not make talaq depend on the relatives’ written permission, on prior payment of the whole dower or on registration.