There was significantly more screen bezel back then, giving cases enough space to curve around and latch onto the front of the device. It would seem the bezels on the iPhone 12 are too small to allow cases to wrap around and grip effectively in the same way as before.

From the Tweet (and also having had those phones): The cases on iPhones 4 and 5 had a lip over the screen, this was not an issue because bezels were large and there were few swipe gestures. However the iPhone 12 cases do not go beyond the screen.