It’s never celebrated/observed on the same day unlike your birthday or Jesus’ birthday (I know it’s not really the 25th of December, but it’s always celebrated in the 25th).
People are just mourning Jesus’ death on a random day just because it’s Friday lol
people want to do social rituals with the seasons. religions just write their name on them and make it about their stuff.
if they didn't claim some big deal ritual in the spring, some upstart nature worshippers would kick off and eat into the Christian's numbers.
like who would be going to church for a regular old sermon while there's people getting shithoused on ferments and lichen with blue face paint, gyrating around in the woods, hooting at the sky and listening to Orbital, The Blue Album.