What is the reason for the Prophet (peace be upon him) commanding his Companions to perform Hajj Tamattu', even though some of them had brought sacrificial animals, and his commanding Ali ibn Abi Talib to perform Hajj Qiran because he had brought a sacrificial animal?

It is established in the Sunnah that the Prophet (peace be upon him) commanded those of his Companions who had not brought sacrificial animals (hady) to change their Hajj into an 'Umrah. Those who had brought the sacrificial animals remained in their state of ihram until the end of the Hajj – as the Prophet (peace be upon him) and Ali ibn Abi Talib (may Allah be pleased with him) did. The Prophet (peace be upon him) said: "If I had known earlier what I know now, I would not have brought the sacrificial animal and would have made it an 'Umrah. So, whoever among you does not have a sacrificial animal with him, let him exit his ihram and make it an 'Umrah." And the people exited their ihram except the Prophet (peace be upon him) and those who had sacrificial animals with them. When Ali arrived from Yemen with the sacrificial animals, the Prophet (peace be upon him) informed him not to exit his ihram because he had the sacrificial animals with him.