Christianity did not pinch festivals from the Earth Traditions.Neither was Christianity corrupted by Earth Traditions. 

If anything Christianity is an Earth Tradition.

To celebrate a festival of light in the middle of winter, to mark solstices and changes of seasons, to note the turning of the year, these things no more belong to one particular religious tradition than name giving, weddings or funerals. 

Christianity is rooted in Judaism, which, with its lunisolar calendar reflected the agricultural year of the near East. The language of land, seasons and former and latter rains, seed time and harvest, run throughout the Old Testament and into the New. To understand more fully we only need to turn to the Wisdom of Solomon 7:15-22 :

May God grant me to speak with judgement,
and to have thoughts worthy of what I have received;
for he is the guide even of wisdom
and the corrector of the wise. 
For both we and our words are in his hand,
as are all understanding and skill in crafts. 
For it is he who gave me unerring knowledge of what exists,
to know the structure of the world and the activity of the elements; 
the beginning and end and middle of times,
the alternations of the solstices and the changes of the seasons, 
the cycles of the year and the constellations of the stars, 
the natures of animals and the tempers of wild animals,
the powers of spirits and the thoughts of human beings,
the varieties of plants and the virtues of roots; 
I learned both what is secret and what is manifest, 
for wisdom, the fashioner of all things, taught me. 

The celebration of the wheel of the year is as intrinsic to Christianity as it is to other Earth Traditions. But as Christianity has spread there have been adjustments to accommodate the pattern of the year for different climates and latitudes. So our current liturgical year includes a mixture of  days, some tied to lunar cycles, others fixed to dates. It may not be how we would design it, and it doesn't make a lot of sense in the southern hemisphere, yet authentic Christian faith has always recognised the preciousness of creation and its patterns.

The rejection of this strand in the weave of Christian practice is recent, and in the West stems from post-Reformation shifts in culture, lifestyle and belief. The growth of the secular and urban living. Suspicion of the supernatural and mystery, in the sacraments of the church and in the sacrament of creation, has dominated.

Imagine if Christianity stopped taking funerals, celebrating new children, blessing marriages.

The loss to the rhythm of Christian faith is that significant. My hope is that Steve and others work will help Western Christianity rediscover this aspect of it faith and practice. That festivals that were once part of our natural rhythm are once again, not just found in Fresh Expressions, but in every Parish. There are already official liturgies available for many of them in Times and Seasons - although strangely that never made the papers!