Why did Jehovah's Witnesses not use the Passover this year to celebrate the memorial, as has been their tradition since Jesus instituted this to celebrate his death ?
"Jehovah's Witnesses commemorate Christ's death as a ransom or "propitiatory sacrifice" by observing the Lord's Evening Meal, or Memorial. They celebrate it once per year, noting that it was instituted on the Passover, an annual festival. They observe it on Nisan 14 according to the ancient Jewish luni-solar calendar. Jehovah's Witnesses are taught that this is the only celebration the Bible commands Christians to observe."
The year 2016 poses a unique set of circumstances as to why the Jewish community has decided to defer the celebration of their Pesach to such a late date this year. The Jewish Passover is to be commemorated on April 23 2016 starting at sundown!
The Jewish calendar follows a lunar cycle calendar, which comprises of some 354/355 days. Since the lunar calendar is about 11 days shorter than a 365-day solar calendar, it is necessary to added an extra month every so many years to realign the two calendars! This is what is happening this year.
The Jehovah's Witnesses have apparently decided to keep the first possibility of celebrating the Commemoration of Christ's Death on the first possibility after the first full moon after the spring equinox (March 20/21), which falls on March 23 this year.
Nevertheless there are some communities that feel that the Jewish community should have chosen another year than 2016 to add the extra month than 2016 to realign their calendar and moving their Pesach to such a late date.