The Prophet Nūḥ lived on while generation after generation passed and increased in their disbelief and transgressions
Allah ﷻ gathered knowledge for all prior ˹nations˺ for Nūḥ and strengthened him with the Rūḥ (Holy Spirit). He then invited his nation ˹to Islam˺ privately and publically for nine hundred and fifty years. Any time a generation passed and ˹the next˺ generation followed them in their ˹corruption˺ and thus they increased in disbelief and transgression.
جَمَعَ رَبُّنَا ﷻ لِنُوحٍ عِلْمَ الْمَاضِينَ كُلِّهِمْ وَأَيَّدَهُ بِرُوحٍ مِنْهُ فَدَعَا قَوْمَهُ سِرًّا وَعَلَانِيَةً تِسْعَ مِائَةٍ وَخَمْسِينَ سَنَةً كُلَّمَا مَضَى قَرْنٌ اتَّبَعَهُ قَرْنٌ فَزَادَهُمْ كُفْرًا وَطُغْيَانًا