Answer: To a great extent, the enticing part is the feeling that one is looking at something private.
Explanation:
A greater part of the allure of the diary is the feeling that you are gazing at something private, something that you that wasn't meant to be seen. Pepys would have not included details of his excessive meal alongside careless depiction of how the rest of London is burning if he had realized earlier how widely his diary would be read. Thus, reading it is as fun as hearing an interesting secret always is with the added advantage that the victim is dead a long time ago and cannot be accused in return or be inflicted with pain.