﴿ فَتِلْكَ بُيُوتُهُمْ خَاوِيَةًۢ بِمَا ظَلَمُوٓا۟ ۗ إِنَّ فِى ذَٰلِكَ لَءَايَةًۭ لِّقَوْمٍۢ يَعْلَمُونَ ﴾

“and [now] those dwellings of theirs are empty, [ruined] as an outcome of their evil deeds. In this, behold, there is a message indeed for peo­ple of [innate] knowledge –”

So those then are their houses lying deserted khāwiyatan is in the accusative because it is a circumstantial qualifier the operator of which is the import of the demonstrative pronoun tilka ‘those’ because of the evil which they did that is their disbelief. Surely in that there is a sign a lesson for a people who have knowledge of Our power and are thus admonished.