>Why didn’t the Ottoman empire, which was Sunni Muslim, assist those helpless Sunni Muslims in Iran and elsewhere?

First of why would they? I know they were the Caliph but we all know that was basically just another hat the Sultan thought would be cool to wear alongside being emperor of the romans and all.

Second of all a rival empire on your borders intervening to "protect religious minorities from persecutions" would be ground for considering those groups disloyal and justifying a genocide against them, which is something the Ottomans would do themselves to christians.

In fact this is not new, the Roman Empire proclaimed themselves the protector of christians in the east and this pissed off the Sassanians to an endless degree and just invoked persecutions. Those were Zoroastrians but the pattern repeated itself regardless of what religion was actually dominate in the area. Zoroastrian, Christian, Sunni, Shia, didn't matter.