Why are all Buddhas unwilling to leave behind teachings when they attain buddhahood in worlds similar to the Saha world?

Once you attain the third or fourth fruit and have eliminated the afflictions of greed, hatred, and delusion, when you look at sentient beings your state of mind will be completely different from how you view them now. There are many things you would no longer say, because saying them would be useless—just like a university professor looking at kindergarten children, feeling that they are truly beyond teaching. When you become a Buddha and observe the multitude of sentient beings, all awash in the afflictions of greed, hatred, and delusion, so utterly foolish, you will likewise feel that expounding the profound Buddhadharma to such beings would be simply unimaginable—it would be no better than playing the lute to a cow. When one is at roughly the same level as sentient beings, one does not feel anything particular about them at all; but once one transcends that level and leaps up to look down from above, that state of mind is something you all could never understand or even imagine, and so speaking of it is useless. The Buddhas, Bodhisattvas, and noble ones have no true companions and are very lonely; sentient beings cannot understand them, still less can they fathom the state of mind of the noble ones.