I'll bet the answer is "Predominant Wind" for a given field. At our field, we most frequently take off left to right, so most of the time people fly a counter clockwise pattern. We have some fliers who really do have a hard time flying the other direction. As an instructor, I always change things up for my students and force them to make both left and right turns.
But having done a lot of learning flying slope soarers, given my druthers, I find I tend to fly in a figure 8 pattern, always turning away from the flight line. These things become ingrained into your brain. I haven't flown a sloper in over 30 years but I can't get that pattern out of my head.
Dave