I worked at a company that had effectively no physical security during work hours until the second time someone came in during lunch and stole an armload of laptops. Then we got card readers and a staffed front desk, and discovered our snack budget was too high because people from other companies on other floors were coming to ours for snacks too. I never felt the office was insecure, except in retrospect once it was…
I once worked at a place where the receptionist held the door open for a thief who made off with about 10 PCs, taken from random work desks near the entrance. She thought that because he was wearing a suit and a badge from his "company" that he must have been supposed to be there, and assumed he was probably taking the computers away to be fixed. There was surprisingly little repercussion for violating the "one card…
Presumably because "everyone" knows that "noone" complies with those policies, in part because it's socially awkward to e.g. close the door on someone who tries to tailgate, and so it needs to be heavily and consistently enforced before it becomes more socially unacceptable to be the person who potentially puts their colleagues at risk of disciplinary actions than to be the person who tells someone they need to swipe.