The whole evacuation time requirment is rather unrealistic. I was watching a segment on the evac certification on the A-380, and it was done with healthy folks, indoors, think they were paid, and all were wearing comfy sports gear, without bags, and were well briefed. Most importantly they knew why they were there, and had a clear goal of beating the time requirment.
Throw in a surprise evacuation, with zero warning, passengers of all ages/builds/health, bad weather, perhaps no verbal order or delayed order, coats, panic, bags, some doors slides not available, (yes I know the tests disable some egree points) etc.
Human nature is the largest problem, many folks are going to grab their purse or backpack and since it likely carries some important stuff it can be understood (not to say it is worth your life). It would likely be days until they got their stuff back, if it survived. I'll leave my wheelie bag, duty free bag and coat behind thanks- (some won't).
Airlines and their bag fees have made the problem much worse. Thank you to Southwest and few others for bucking this trend.