Following-up to these [previous][1] [questions][2], why do some traditions *not* celebrate the birth and death (or, more accurately, His resurrection) of Christ as "official" church "events"?

I understand that celebrating the Communion Table is a celebration of Jesus death - but why not celebrate His birth and resurrection, too, in a "special" way (ie beyond just celebrating His resurrection every Sunday by that being the the church comes together for worship)?


  [1]: https://christianity.stackexchange.com/q/2666/69
  [2]: https://christianity.stackexchange.com/q/4772/69