It had to do with the number of dimensions and combinations that were being looped over. That kind of scale difference generally comes from combinatoric explosion -- exponential or high polynomial time vs linear or log-linear time.

The rewrite realized an approximation was reasonable in place of a more "correct" algorithm.

Note that I'm not saying Python was the cause, but the ease of reading and writing code may have helped the programmer come to this algorithm. Instead of stressing about bugs and deadlines. Algorithm choice seems correlated with language choice, in my experience.