I get the feeling they anticipate a scenario where citzens take matters into their own hands, and the MM leadership does not want to be blamed for what is out of their control now, and to come
Check the link in reply #5 - they were promoting actually detaining people, which under AZ law would have been potentially criminal - to effect a ciizens’s arrest, you have to have witnessed a felony or have solid reason to believe the person had just committed a felony - and most illegal crossings are not felonies, which would make the detentions illegal arrests. Methinks someone gave them sound legal advice and they are backing away from doing that by simply not going.
I also have a feeling that Hayworth’s campaign reached out to Simcox and told him they don’t want the Minutemen escalating their methods during the election, which could have given McPain propaganda material against the border control/anti-shamnesty advocates.