If God punished the people for their sins, He would not leave a single creature on earth. But He respites them for a predetermined interim. Once their interim is fulfilled, then God is Seer of His servants.
وَلَو يُؤاخِذُ اللَّهُ النّاسَ بِما كَسَبوا ما تَرَكَ عَلىٰ ظَهرِها مِن دابَّةٍ وَلٰكِن يُؤَخِّرُهُم إِلىٰ أَجَلٍ مُسَمًّى فَإِذا جاءَ أَجَلُهُم فَإِنَّ اللَّهَ كانَ بِعِبادِهِ بَصيرًا
wa law yu’aakhizul laahun naasa bima kasaboo maa taraka ‘alaa zahrihaa min daaabbatinw wa laakiny yu’akhkhiruhum ilaaa ajalim musamman fa izaa jaaa’a ajaluhum fa innal laaha kaana bi’ibaadihee Baseeraa