As stated before, the point of these Craig movies is to show us Bond going from a green, rookie agent to the world-famous super-spy we've come to know before the reboot within its own universe. Casino shows Bond falling in love and subsequently being betrayed, Quantum further exposes him to the duplicity of the job through Mathis and Vesper and in Skyfall we see him address his past and shake through his uncertainties as an agent to become a more seasoned person.
The death of Judi Dench allows for a male M to slip into the job and Moneypenny gets a bit of backstory leading to her position as secretary which both reference the old Bond movies but do not lend themselves to a linear Bond timeline.