Why Easter is When it is

The date of Easter is changeable because it is one of the only Luna Celebrations we have left. Halloween in its pagan form was originally also a luna celebration because it was the northern European Autumn fest, it was Eastern's opposite number which obviously is Northern Spring but Christianisation blew that. Halloween also was a New Year at one time as well because it originally represented the confrontation and cleansing of dead and other spirits just as the Chinese do it their year change.

Easter is also the only hint left in the modern era that Jesus was a Jew, something of an embarrassment for many Christians, because it is still based on Passover, one of the most important holy days in their Luna calendar. So they make the date for Easter this way: it is the first Sunday after the first Full Moon after March equinox (when day n night are equal between 21st n 23rd depending on the year). So the earliest it can be is the first week after that date and latest is the fifth week after, depending on the coincidences. As we saw between this year n last it can jump around quite a lot. We, in the south, are still trying to figure out how to cope with the seasonal differences so we have harvest festivals like the Royal Easter Show in Sydney - which in the the North would be in October (OktoberFest being a famous example) designed celebrate the ending of the preparations for winter - it might be said that Australia's festival season the Adelaide, Melbourne n Sydney' mardi gras are the closest we get to Autumn festivals. The Sydney Festival is more a mid-summer festival, probably there for commercial reasons because the city used to empty so thoroughly in the summer businesses wanted people to stay around so they could keep trading. Then we have the spring festivals in October n November, the most famous being the Melbourne Cup, but there are those in local communities across Greater Sydney and other cities (being a Sydney Person, sadly, I'm not up on whether these kinds of local festival are common across the country, though there are spring races all over).

Australia's seasons are too complex and too subtle compared to Europe that it's harder to figure out what and how to celebrate the seasons. Also being very urban nature's grosser time markers like the solar cycle, the year and seasons, have gradually become less important at the same time we started our invasion/settlement. City living separates us from these cycles.