Why do Human Incarnations not perform miracles that are big enough that they cannot be denied?

[Shri Durgaprasad asked: Pādanamaskāraṃ Swāmi! A person who believes in God Datta, but not in the contemporary Incarnations of God, said that in the past, God’s Incarnations were not recognized or were seriously doubted by Brahmā, Indra, Kaṃsa and his army, KālÄ«ya, and Manmatha. But God did not deny their doubts. Instead, He removed their doubts by proving His divinity. This person said that if a claimed Incarnation like Sathya Sāī Bābā were to manifest a couple of large pumpkins or watermelons, not only would he surrender to the Incarnation, but that he would also bring all his relatives and friends to surrender to Him! But he says that Bābā only manifested ashes and no large objects. He wonders what disturbance in the karma cycle would be caused by manifesting a few pumpkins. But manifesting such big objects would immediately remove all the doubts of devotees. He does not believe that any claimed Incarnation would be able to create such large objects and prove His divinity. Please enlighten me on how to respond to this person. At Your lotus feet, - Durgaprasad]

Swāmi replied: O Learned and Devoted Servants of God! I have seen with My own eyes, Śrī Satya Sai Bāba creating a big glass basket that was held in His two hands. The occasion was Kṛṣṇāṣṭamī and the basket contained various kinds of sweets. Bābā said that He had brought those sweets from Mathurā city. On another occasion, Bābā held a small pot upside down and moving His hand in the inverted pot, He produced ash in such a huge quantity that it could have filled several gunny bags. The streams of ash produced were being showered on the statue of Shirdi Sai Bābā. I also saw a very big and long golden ornament created by Śrī Satya Sai Bābā, which He presented to Smt. Anjali, a very strong devotee of Bābā. So, do not draw conclusions based on your limited observations and limited knowledge.