Why unlike Umar, did the Prophet (pbuh) left Mecca for Hijrah secretly ?
Because as his (prophet) actions are (تشريعي) law for the Ummah, he did chose the easiest option for everybody (persecuted) because not everybody is like Umar (ra) in courage and strength.
Peace be upon you oh Prophet of Mercy
Al-Faqir Al-Habib Mouhamed Mountakha Sakho Tidjani