What does it say about a person if they never get up before noon?
If they are the first person to exist, it probably says that morning was for some reason a convenient time to sleep.
If they live in parts of modern society, it might say that they are lazy and weak willed.
How did getting up at one time or another come to signal laziness? You still have to get up once per day.
One story I can imagine is that originally there was some weaker reason to get up early. For instance if your work benefited by sunlight, you could get a bit more in. And then since that was a reasonable thing to do, people who didn’t do it looked like they were less good at getting up. Which made getting up early even better thing to do, so that everyone knows that you can.
And then people who had been on the fence before about whether to bother getting up early started to find it worth their while. Making the remaining noon-sleepers even more weak willed on average. And so it continues, until sleeping until the afternoon strongly suggests laziness.
In general, if an action is a tiny bit good, not doing it can look a tiny bit bad (or stupid, or lazy, or incapable). Which makes it better to do, which makes it look worse to not do it, and so on. And maybe in the end the speck of good that started this disappears, but the value of sending the signal if you can is enough that the equilibrium is stable.
Does this actually happen?