At last, a Purge movie that has some semblance of logical consistency in the motivations of the NFFA!

It's still stupid logic, but at least it's coherent. Here it's pretty firmly established that purging as a concept does not work, and the NFFA knows it does not work. The metric by which the purge is understood to work by the people in this universe is number of people murdered on purge night, and because not enough people are murdering each other on their own the NFFA steps in to boost the number of murders. Apparently if not enough people are murdered the NFFA will get voted out of power. An offhand comment at one point indicates that the general populace wants lots of murders because the country is overpopulated and purge night will help alleviate that (though there's no real indication or example of how overpopulation is an actual problem in any of the films so far, including this one).

By omitting the weird out-of-place NFFA members and followers who cultishy get off on watching and partaking in sadistic torture-murders, The First Purge is probably the most "realistic" and logically consistent purge movie we've had so far, and it's also pretty fun to watch. Best one so far, in my opinion.