Internal reasons for the decline of the Mughal empire: The impact of Aurangzeb's policies on the stability of the Mughal Empire. The effectiveness of his successors as rulers. Problems of controling the Empire. The rise of the Maratha and Sikh Empire.
This is true that the Mughals were pleasure seeking but this was not the main reason for their decline. The weakening of the army plus the attacks from the Persians are the main reasons for their decline.