Not sure, but one series is IKF sanctioned. The other is tied in with USOpen. Definitely some difference in tires. Not sure on motors. I also think that the IKF series is all on the front range and probably set up for people who don’t want to travel long distances. GJMS is several hours from the Denver area over the Rocky Mountains. The other tracks are all within 2 hours of each other at the most.
It is possibly better than one big series. The 2 series race dates do not compete. One has 8 dates and the other has 4 dates which gives the racer a lot of control over how much racing they want to compete in. Plus having 2 series competing for racer turn out produces more awards for the racer rather than awarding 1 series control over all the races and racers.