This is the 16409th most frequent Turkish word.
yatmadığını
"That [he/she/it] did not lie down/sleep."
Here, 'yatmadığını' refers to the fact that Ali stayed awake and did not engage in the act of laying down to sleep.
Ali'nin gece geç saatlere kadar çalıştığı için yatmadığını söylediler.
They said that Ali didn't go to bed because he was working until late at night.
In this sentence, 'yatmadığını' indicates the ongoing state of not having gone to bed due to being occupied with thoughts.
Onun, önemli bir olayı düşündüğü için henüz yatmadığını tahmin ediyorum.
I guess that he hasn't gone to bed yet because he is thinking about an important matter.
'Yatmadığını' in this context emphasizes the continuous state of the house residents staying awake as inferred from the external observation.