[dfxm12]

I don't think it is odd at all. In a choice between "our religion can't gain the membership to survive" vs "ok, we can bend the structure of our religion a little to make it more palatable for this huge amount of people", I think the choice is obvious.

You might find it odd that Christians think they came up with Easter (or Christmas, or the Epiphany...) though.

[eitland]

With Easter, unlike Christmas, there isn't the same doubt about which time of year it was as it was around the time of the (much) older Jewish Passover celebration.

[bashmelek]

A lot of these things come from folk practices that the Church would permit but then direct towards something acceptable.