[NextUserName]

Two reason that I can guess (before reading any comments or the article).

1. More energy is lost the wider the loop is. This is because on a truly round loop, the cars would be pushing hard against the widest part of the circle as the cars change from going from right to left (or vise-verse). By not going out as far, you don't have to come as far back to get to the top of the loop.

2. The geometry of the loop is tuned partially based on the number of cars. Most roller coasters have between 6 and 10 cars. You want the first one to be starting on the way down way before the last one all the way to the apex. This uses gravity to help with overall velocity. The easiest way to achieve this is by distributing the sharpest part of the angular transition at the top of the loop.

Perhaps I should not post a comment before reading, but I am curious to know what others think (off the cuff).