If I remember correctly, security at DD is a relatively new thing and used to be for the parks only, but it got annoying for those going to DD then back to the parks over and over again, so they just kept expanding the security lines. Over time, they were able to construct paths and close open areas to make it work. It took a lot of trial and error as the security spots were always moving, but I think they finally got it down perfectly in a way that makes sense for everyone and isn't a total hindrance (unless the park gets slammed on crazy event days, which still happens and is just the nature of the beast). However, things will change again once the new park starts construction.