Crazyguy, I asked the same question myself five years ago and did some investigation. What else dies for three days? It is the sun which 'dies' for three days from the 21st December to the 24th. It stops at the same point of the horizon, setting and rising there for three days and three nights but when It rises again on the 25th December it has begun to move northwards again; otherwise described anciently as being "reborn". This was a cause for celebration; the re-birth of the sun.
Just to get the astronomy right-- the setting point of the sun was a calendrical marker for the seasons for pre-literate agriculturalists possibly starting in the New Stone Age, (may be earlier) and going forward for some thousand years through the Bronze Age and into the Iron Age. Where else would you look to find what the date is without books or calendars? How else would you know when to sow particular crops? The position of the sunset on the horizon tells you. Furthest North is midsummer and midway are the equinoxes.
In Autumn the position of sunset progressively moves southwards on the Western horizon until it slows down in its southern travel and stops altogether for three days. On the 25th December it begins to moves North once again. If you live on the equator this will not help you and neither will it be of use if you live in the Arctic. In between these geographical extremes you would have depended on this information for your farming and therefore your food. It would not be surprising to celebrate the turning of the seasons and clearly the feast and fast days of the ancient pagans were absorbed into the Bible and sanitised by early Christian Church. It's one reason why Jdubs have the memorial. . .
Many of the Stone circle alignments (but not Stonehenge) even in the north of Europe eg Maeshowe in Orkney Scotland, are orientated for a solar alignment at sunrise on the 25th December. It was the moment to celebrate the return of the Sun, the rebirth of the Sun God who would bless the community again with light and growth and fertility in the fields and hence the continuation of life itself.
In the Neolithic folk calendar Christmas day was central to the annual cycle of life to be followed three months later by the sacrificial death of the son of the Sun God at Easter.
In Homer, Ulysses goes down to the underworld for three days, in fact all saviour and celestial heros die for three days as a mark or badge of the God-man. Jesus was described as doing the same so the listeners would know what character he was meant to be.
Jesus is none other than a historicization of the folk tale of the journey of the Sun God as were all of his literary forebears, Dionysus, Attis, Horus, Adonis et al.
It was the fact that early Christianity preached that this god-man Jesus had become a real breathing person, who had lived -- and died for three days and three nights and was resurrected according to the folk tales of old, which shocked the sensibilities of the educated Greeks and Romans to learn that they gullibly believed these outrageous impossibilities.