An internal investigation of the TSA, leaked in 2015, found that many types of explosives apparently look to agents quite a bit like chocolate. Guns seem to closely resemble Tom Clancy novels in their eyes. Knives may be easily mistaken by the thin uniformed line against especially dim terrorists for those fuzzy troll dolls, though that part is a bit unclear. Well, maybe that's not all true. But such confusion would explain why "TSA agents failed 67 out of 70 tests, with Red Team members repeatedly able to get potential weapons through checkpoints."
After that embarrassing failure, the TSA's working theory seems to be, if you make everybody dump their sandwiches, tablets, and paperbacks into separate bins at the security checkpoint, we vastly increase the chance of intercepting backpack nukes and rocket-propelled grenades, which themselves could be mistaken for sandwiches, tablets, and paperbacks. Sure, the guards may still need some guidance as to which confiscated items are safe for noshing, but the security measures will be covering all bases.
Speaking as a world traveler [snooty much?], the TSA employs some of the thickest agents that I've ever seen anywhere in the world. Israel is tops; Australia is interesting, as their agents are quite jolly and yet are scrutinizing everything about you and your belongings. The TSA reacts with the emotional fragility of petty authoritarians left unchecked for too long.