That's because according to studies (which is also in Matthew Walker's book) about 15-20% of the population has a different chronotype - a genetic night owl if you like (I'm one of them).

We are hardwired to increase in cognitive abilities and energy as the day progresses, peaking in the evening, and for some, late into the night/wee hours of the morning.

A typical night owl has the lowest energy and cognitive ability at the point of waking - opposite to the other 80% of the population.