...the underlying premise just doesn't make any sense. According to the story, the government instituted the purge in order to save money on the prison system (iirc) - well, except that the damage done every year during the purge (especially all the medical care after the fact) would be in the hundreds of BILLIONS - how is that a good outcome for the government?
The less you think about "The Purge" concept, the better. Trying to go further and further into its origins, etc. only makes the series tougher to accept, not make it easier.
Each installment since "Anarchy" has worked less better than the one that came before it. I think that "Anarchy" got it best, following someone who was going to purge, and finding him rethinking what he was going to do, and instead helping others escape the violence. I think that, after doing that, there wasn't much of anywhere to go with the series.