That's because when you actually need the handgun you'll want it to function as expected when you pull the trigger. A safety is just extra complication that provides no significant benefit if you're already handling the firearm like you're supposed to (which is to say, never pointing it at anything you don't want to destroy). Even without external safeties, modern firearms often do contain internal safeties to ensure that they only go off when the trigger is operated, as opposed to being dropped or something.