Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(How many generations) of old (have we destroyed since Noah!) since the people of Noah (And Allah sufficeth as knower and Beholder of the sins of His slaves) that they were destroyed even We have not explained this to you; and We know their sins and chastisement.
How many — in other words, many — generations, communities, We have destroyed since Noah! And your Lord suffices as One Informed and Beholder of the sins of His servants, Knower of the hidden and manifest aspects of these [sins] (bi-rabbika, ‘your Lord’, is semantically connected to bi-dhunūb, ‘of the sins’).
Warning the disbelievers of the Quraysh for rejecting His Messenger Muhammad, Allah says that He destroyed other nations who rejected the Messengers after Nuh. This indicates that during the centuries between Adam and Nuh, humans were following Islam, as Ibn `Abbas said: "Between Adam and Nuh there were ten generations, during all of which humans were following Islam.'' The meaning (of the Ayah) is: "You disbelievers are not more dear to Allah than they were, and you have rejected the most noble of the Messengers and the best of creation, so you are more deserving of punishment.''
(And sufficient is your Lord as All-Knower and Seer of the sins of His servants.) means, He knows everything they do, good and evil, and nothing at all is hidden from Him, may He be glorified and exalted.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
Here a definite form of Divine procedure for the destruction of a people has been stated. When the well-to-do people of a habitation become disobedient, it is a portent that it is doomed to destruction. After their persistent and continuous transgression, the well-to-do people become so obdurate in their disobedience that they begin to discard the instinctive dictates of their conscience. The same thing has been stated in v. 16: "When We decree that a habitation should be destroyed We give Commands to its well-to-do people and they show disobedience." This is because Allah has created conscience for the guidance of man. Therefore, the dictates of conscience are really the commands of Allah. Thus it has become quite obvious that by "When We decree that a habitation should be destroyed" is not meant that Allah intends to destroy it without any reason. It is destroyed because after their disobedience "that habitation incurs Our just wrath and We totally exterminate it." The habitation deserves such a punishment because its common people follow the well-to-do people who are the factual leaders of a community and are mainly responsible for the corruption of the community. At first the well-to-do people commit acts of disobedience, wickedness, mischief, cruelty and tyranny and then the common people follow them and incur the torment of Allah. Incidentally, this is a warning for every community that it should be very discreet and prudent in choosing and electing its leaders and rulers, for if the latter are mean and wicked, they will inevitably lead the community to destruction.