During the spring and summer months when it is nice outside, most people aren't sitting in front of the computer shopping on the internet.  The coin market would be edged towards 'over the counter' sales at coin shows or shops as people travel around during the vacation season.

During the winter however, when it's cold and dreary outside, people would rather sit in the comfort of their own home looking for the best deals on the internet.  It is proven that the winter months net the highest sales for internet coin sales.