Jesus' disciples knew well that the Teacher was under close watch by the Pharisees and elders. What He preached did not fit in any way into the usual framework of their religious ideas. It was simply dangerous for Him to approach Jerusalem. The apostles repeatedly tried to dissuade the Teacher from coming to this city. Their fears were truly serious, since they considered going with Him to Jerusalem equivalent to death.
That is why it is so surprising that they so willingly and obediently go at Jesus' request for the donkey on which He is to enter the city. Most likely this is connected with the faith in Him as Messiah that spread after the raising of Lazarus, who had been four days dead. Evidently it seemed to them that the very time had finally come when their Teacher would show His true power and reveal the promised Kingdom. And then it is understandable why they justify themselves before the owners of the donkey without a shadow of doubt, saying simply that the animal is needed by the Teacher. One can justify oneself this way only if one's mentor is, at the very least, nearly a great ruler. And their expectations were justified, but not at all in the way they thought. Because His Kingdom turned out to be not of this world at all.