I wouldn't call it the Pagan WOTY. It's the Wiccan WOTY actually. Paganism is too broad a term; most Pagan religions have different holidays, they don't celebrate a universal model, though many modern Pagans have adapted the WOTY in some way.
Most of the holidays are somewhat based on earlier Germanic and Celtic holidays, but basically in Wicca it's a celebration of the cycle of the seasons, and the way they reflect in the cycles of our lives.
Wicca is a synchretic religion (like so many religions that have come before it). It's a modern reconstruction/reinvention of older beliefs and practices.
Originally Wiccans only celebrated the 4 major sabbats but the 4 minor sabbats were adopted to recognize the solstices and equinoxes later.