The three great annual festivals of Hebraic religion are Pesach (Passover) and the accompanying “feast” of Unleavened Bread; Shavuot (Weeks), also called the feast of Harvest (or First Fruits); and Sukkot (Booths), or the feast of Ingathering (end of harvest). The feasts of Unleavened Bread, Harvest, and Ingathering are clearly agricultural in origin while Passover is pastoral, welded onto the head of the agricultural festival.
The earliest text for the Shabbat mandate gives no religious reason for its prescription. Rather, it was to give servants and animals a break from their labors. Only later, after the captivities of the elites of the northern kingdom of Samerina/Beth Omri in Nineveh and of the elites of the southern kingdom of Yehud/Beth Dawid in Babylon that Shabbat took on a religious significance (commemoration of Yahweh’s rest on the seventh day of Creation Week) when those elites adopted the seven-day creation myths of their captors.
Likewise, the three pilgrimage festivals took on new and specifically religious myth meanings when the Hebrews adopted the foundation myths found in Genesis and Exodus. The dual festival of Pesach came to symbolize the exodus from Egypt. Shavuot came to symbolize the delivery of the Torah at Mt. Sinai. Sukkot came to symbolize the forty years of wandering in the desert of Sinai.
All of these commemorated events never actually happened, but they are important to the foundation myths. To cite an example with which I am familiar, it would be like the Irish commemorating the flight of Scota, daughter of Pharaoh and her husband Goidel Glas from Egypt, the landing of the Milesians at Inver Sceine in west Munster, and the defeat of the Tuatha De Danaan at the Battle of Tailtiu and the subsequent exile of those foes underground as the Daoine Sidhe.
Back in West Asia, one of the midrashim about Shavuot is that when Yahweh gave the Torah to Moses, he did so in all seventy-two languages spoken on Earth, at least according to Hebrew tradition. In Canaanite mythology, El, the supreme god, had seventy-two sons, each of them the god of their own people of Earth, each of which spoke its own language. The story of Pentecost (the Greek name for Shavuot) in The Acts of the Apostles in which all present understand the words of the apostles regardless of their language reflects this midrash.
As a time of expectation (as well as inconvenience), Sukkot acquired religious significance additional to the Wandering. It became a time of looking for the Messiah, specifically the Messiah ben David as opposed to the Messiah ben Joseph. This is the aspect of Sukkot which ties into the Passion Story in all four gospels.
Jews, Galileans (in the 1st and early 2nd centuries there was a difference), and perhaps Samaritans converted to the new Way mythologizing the real events of the life of the one to whom they claimed allegiance would have done so in imagery drawn from their own culture. Hence, the waving of palm branches and the Hosannas upon Jesus’ entry into Jerusalem, because these two things are part of the anticipatory, messianic-looking festival of Sukkot.
To have Jews, Galileans, and other pilgrims waving palm branches and shouting “Hosanna!” at Pesach would be like Christians erecting Christmas trees and singing carols in Holy Week.
I suspect that the myths surrounding Jesus of Nazareth and his death as a rebel at the hands of the Roman state prior to the Great Jewish Revolt of 66-73 CE placed these events at Sukkot, given its connection to messianic expectation and palm branches and Hosannas, when Jesus was shrouded in purple to return as the conquering King of the Jews. After the epic fail of the chauvinist militants in the Siege of Jerusalem, Christians sought to deemphasize those political aspects and moved the Passion Story to Pesach, a time of intentional sacrifice.
Many of the sayings of Jesus, if accurate, indicate that instead of the Messiah ben David, he saw himself more as the Messiah ben Joseph, who would precede the former and die in self-sacrifice.
Whoever put the Passion stories of the various gospels into their current form, they clearly were not Palestinian, even if they were Jews, Galileans, or Samaritans and not Gentiles. One can understand, perhaps, why they couldn’t let go of the imagery of the story of the triumphal entry into Jerusalem, but it is out of place.