I agree with all these... USH has way, way more entry points that Orlando does. And doesn't Curious George parking have an upper level access? Not to mention the pedestrian entrances coming up from Lankershim/Metro area, that's at least two more areas (one by the fountain/part exit, and one from the bridge) that would be difficult to just shut off without creating either logistical nightmares, huge security line back ups, really ugly barriers, or all the above.
That said, when Citywalk first opened up after Covid, they did move security to the parking garages, and they did cut off some access points. At the same time, the crowds were decidedly a lot fewer, so whether that same plan could work scaled up to the crowds of now, I have my doubts.