I actually remember exactly when they changed the policy. It was the 2016 season, right after the terrorist hid bombs in Seaside Heights, Manhattan, and Elizabeth? train station garbage bins. If my memory serves, water bottles were banned immediately thereafter, and by the 2017 season that included outside food as well.
The fact that the language in the policy (referencing horsesh*t DHS guidelines that have no basis in logic or consistency with many other venues as the reason) is largely unchanged since then tells me that the immediate 'safety concern' was used as an excused to permanently eliminate outside food/drink in the hopes of boosting concession revenues.
The additional fact that us diehards/season ticket holders actively and openly discuss how we are able to bring multiple water bottles and snacks into the stadium anyways, as well as the hot-weather debacles the past 2 seasons with people passing out from dehydration, is indicative of how this issue has been mishandled, and arguably serviced to piss off ticketholders more than raise revenue for the program.