One thing emerges clearly from the entire tradition: Essentially, this farewell meal was not the old Passover, but the new one, which Jesus accomplished in this context.

Even though the meal that Jesus shared with the Twelve was not a Passover meal according to the ritual prescriptions of Judaism, nevertheless, in retrospect, the inner connection of the whole event with Jesus’ death and Resurrection stood out clearly.

Therefore, it was Jesus’ Passover - and in this sense He both did and did not celebrate the Passover:

The old rituals could not be carried out — when their time came, Jesus had already died.

However, He had given Himself, and thus He had truly celebrated the Passover with them.

Furthermore, the old was not abolished; it was simply brought to its full meaning (Jesus of Nazareth, p. 114).

Graciously, how beautiful it is to know that Jesus’ Passover continues in our Holy Mass.

Pope Benedict

There is nothing in scripture prohibiting a Christian from celebrating any Jewish holiday, as long as they do not do so to be justified by God (Gal 5:4). However, just like Americans don't celebrate Cinco de Mayo (at least legal ones) or Boxing Day, holidays of other countries, most Christians see no sense or purpose in celebrating old Jewish holidays.

They celebrate The Last Supper which was a Passover observance.

The passover myth sheds an interesting light on pre-Deuteronomic (polytheistic) Hebrew beliefs. Yahweh, the Great Angel in the form of the 'angel of death' takes his rightful sacrifices of the first born infants. The Baal-Moloch sacrifice we also see in some older versions of the Isaac story.

The passover is a Jewish celebration, there's been a new covenant in the mercy of Christ since then.

They only cherrypick the parts they like.

Passover is the Ester version of Jewish's.

Passover is of Jewish tradition. Jesus instituted the celebration of his death on Nisan 14 which is Àpril 11 after sundown-Luke Luke 22:19,20

Who cares