The following is part of a chapter from my book Mysteries of Judaism 1 in which I explain that every Jewish holiday, without exception, differs with what the Bible mandates. In fact, several biblical holidays ceased to exist. Passover is one of them.
A dead holiday passed on its name
Unlike Rosh Hashanah and Yom Kippur, the holiday of Passover did not continue to exist in a radically modified fashion with a new name after the temple was destroyed in 70 CE. It disappeared entirely and Chag Hamatzot’s name was changed to Passover.
The biblical Passover
The biblical Passover occurred on the fourteenth day of the first month, later called Nisan. It had only one ceremony. The Israelites were required to offer a Pascal sacrifice and eat it toward the evening of the fourteenth day. This holiday of Passover was followed on the fifteenth of the month by Chag Hamatzot, the festival of (eating) matzot (unleavened bread). The biblical Passover lasted one day. Chag Hamatzot was seven days.
When the temple was destroyed and sacrifices stopped, Passover could no longer be observed and, although it is biblically mandated, was discontinued. However, to remember this holiday, Chag Hamatzot was renamed Passover. The siddur and all prayers associated with Chag Hamatzot do not use the revised name but calls the holiday by its biblical name Chag Hamatzot.
The Origin of the Seder
One of the principle ceremonies of the current Passover holiday is the Seder. It is not mentioned in the Torah. In his book The Origin of the Seder: The Passover Rite and early Rabbinic Judaism (Jewish Theological Seminary Press, 2002), Professor Baruch M. Bokser explains the origin of the Passover Seder meal ritual. He suggests that when the temple was destroyed by the Romans and the Pascal sacrifice could no longer be brought there, the rabbis instituted the Seder, a home ceremony rather than a temple oriented one, and organized a set of procedures that the Jewish family should do at home together. The rabbis minimized the importance of the sacrifice in the Seder so that the people wouldn’t dwell on its loss, for it was no longer significant or relevant.
Unlike the Pascal sacrifice, the Seder was not a pilgrimage rite from home to Jerusalem ending in the offering. The rabbis’ Seder is a celebratory meal at home commemorating the exodus from Egyptian slavery; unlike the biblical sacrificial ritual, the Seder became both a family festivity and an intellectual endeavor; “the narration of the Exodus experience (became) a central part of the (home) ceremony”; the “child’s question (introduced as part of the Seder narration did) not depend on the procedures surrounding the sacrifice and its blood”; the family “uses wine instead of meat from the sacrifice to express one’s joy”; “the unleavened bread and bitter herbs were originally secondary but have been elevated in status equal to that of the Passover sacrifice”; while the Levites monopolized the singing in the temple, all Jews “sing psalms to God; and Jews not only focused on the nation’s past history, but were required to identify their own lives during the Seder “with the Exodus experience.”
Since the new emphasis is on the present and future rather than the past, “the lack of reference to Moses (in the narration) is only natural. While Moses had a role in Egyptian liberation, he does not figure in any of the later instances of redemption.”
About a century and a half later, around the year 200 CE, the editor of the Mishnah, the first Jewish collection of laws and ideas, described the newly-developed home ritual for the first time in writing. The Mishnah tries to cover the fact that it is not offering an innovation, and leaves readers to believe that it is simply codifying “a well-tried and established road.” This Mishnaic ceremony was itself later changed in many ways. For example, the Mishnah has the youngster ask three questions at the Seder, one of which concerned the Pascal sacrifice. This was later amended to four questions, the Pascal sacrifice query was dropped, and two new ones inserted.
Good point that the siddur calls the holiday Chag Hamatzot instead of Passover. That alone proves your point.