It’s human psychology. Imagine you guess the birthday of everyone you meet. Your odds of being right are the same no matter whether you always say “January 1” or if you pick a date that feels right for the person (assuming there is no astrological or other magical sensing).

But getting Jan 1 right would feel like an inevitable event, like you’re testing statistics and, yep, they work. Getting a custom date right would feel like you made a smart choice. Even if you know it’s just the same statistics.

At least I expect most people would feel that, or at least as many as enjoy gambling in games of chance.