Departing Ixtapa airport permanent resident

Just wondering as a 10 year Permanent Resident why you all have to do this. I live in San Juan del Rio, Queretaro and when I leave, I just leave. No trips to the immigration office and will stay gone from anywhere from 3 months to close to a year to work on golf courses here in the USA?? Never had a problem leaving or returning at all and usually get pulled from the single line at immigration once they see my Resident card to get out of the way quicker. Still seeing posts also about the red/green button at the airport?? Hell they got rid of that here almost a year ago, if you have a carry on, they pretty much let you walk out but if bags the National guard is going to xray and go through, but still never any problems with things. Semper ZIH!!!!