The earth is an oblate spheroid to an approximation. It's not that they're not symmetric, but at the equator the north south axis has higher rates of curvature than anywhere else (but the east west has somewhat lower rates because of the larger circumference due to the bulge).

So that large lines of sight are near the equator on a north south axis (or symmetrically south north) is crazy because the high rates of curvature in that direction at those latitudes should give the shortest distance to the horizon on earth, making those lines of sight even that much more impressive!