2. So how do you require a person to run a whole series? Sorry, that just does not make sense.
Look at the entire quote: "requiring the athletes to run all of them to get points and prize money at the end of the circuit." He means that requiring them to run the whole series to qualify for points standings and prize purses at the end of the series is their enticement. Those who want to forgo the entire race series will be gladly supplanted by those who might get less of the per-race prize purse but by consistently placing in the top 10-20 can earn series points and prize money.