What is the wisdom behind the legislation of the Hady (sacrificial animal) and fasting in Hajj for those not residing in Makkah, even though they face greater hardship?

The wisdom behind the obligation of a sacrificial animal (dam) upon the pilgrim performing Tamattu' from outside Mecca, but not upon the people of Mecca, is to give thanks to Allah for enabling him to perform two rites of pilgrimage in one journey, and for granting him the concession to enjoy himself by omitting one of the journeys. Thus, it is a dam of gratitude for the completion of the rites, not a dam of compensation.