My hypothesis is that the people who get majorly affected by blue light at night, are that way because they’re not getting a strong-enough pulse of blue light in the morning for their circadian clock to calibrate itself by. It latches onto whatever signal it can find, and thus begins to think that “sunrise” happens at 9AM when you sit down at your blue-light-emitting monitor, rather than at 6AM when blue light starts coming down from the sky.

Or, shorter: maybe it’s because you have large east-facing exposure in your house.