Things are never so simple and clear cut -- delayed sleep phase disorder is a fairly common ailment. There was a recent paper which studied a mutation that might explain some cases of DSPD [1]. According to [1], a sizeable fraction of the population possesses a mutation such that their circadian clock runs ~2 hours slower (their day is longer) and so have a sleeping pattern which drifts. This usually manifests itself as late sleep/late starts.

https://www.sciencealert.com/scientists-say-they-ve-finally-...

[1] http://www.cell.com/cell/abstract/S0092-8674(17)30346-X