There are two ways to see the 1979 film, The Shining, the first from the vision of its director Stanley Kubrick, and the second, that of Diane Johnson, which fits much more to the vision of Stephen King. Even the vision of Diane Johnson differs from that of Stephen King mainly in the approach to the character of Jack Torrance.
Doctor Sleep, fits as a sequel to the Stanley Kubrick movie, following the vision of Diane Johnson and taking the main lines to the plot of the novel of the same name in 2013, also working as an adaptation of it.
Now, considering that Doctor Sleep, released in November 2019, affirms that particular vision that mixes King's mythology, mixed with the ideas that Diana Johnson gave to The Shining, we can make a very effective analysis of that film, so If you have any doubts, questions or concerns after watching the movie, do not worry, because then and without further ado, we begin the second part of the Analysis and Explanation of The Shining and Doctor Sleep.
The Shining is a psychic ability that allows those who have it to have an open mind to any type of communication. Thus, people who shine, are able to communicate with others using only their mind, either being close or miles away. This ability also allows them to enter other people's minds by reading their minds, and even more, they are able to force other people to perform specific actions. In other words, they would have the same powers as Professor Charles Xavier, in X-Men.
This supernatural communication ability allows them to communicate with things that are not alive, such as the ghosts that are in the Overlook Hotel, and see the past and the future. In Doctor Sleep, we also see that depending on the level of power that the subject has, he is even able to project himself in different places and even at different times and move things with his mind, even miles away.
After Wendy and Danny escaped from the Overlook, they finally ended up in Florida - they didn't want to see snow again - as far as the ghosts of the gloomy hotel reached the boy, attracted by his immense power. However, it wasn't just the Overlook ghosts that followed Danny, Dick Halloran's ghost did too. In fact, it was Dick Halloran's ghost who taught him how to get rid of ghosts, using mental boxes.
Not even Danny knew exactly what was happening with these entities, once he manages to lock them in those boxes. What we can draw in conclusion after seeing Doctor Sleep, is that ghosts can stick like leeches, to the shining of a person, and follow them wherever they go. And that was precisely what happened with the ghosts Danny saw. However, it must be clarified that there are many other ghosts in the hotel that were not attached to Danny's Shining.
When ghosts are locked in the boxes, they simply cannot manifest themselves and are blocked. However, they do not die and do not disappear, in the same way that the photos of your cell phone do not disappear when you lock the phone with a password.
Something that must be understood about The Shining, is that the person who owns it tends to manifest itself differently, even if technically it is the same ability, for example in Andi it is powerfully manifested with the ability to dominate the will of other people, forcing them to do things they don't want to do. However, that does not mean that Andi is not able to move things with the mind and communicate with ghosts, or to predict the future, as Abra or Dan do, it just means that for her the domain of will occurs naturally, effortlessly.
Likewise, in Dan, the glow seems to manifest itself in the form of death prediction, and in fact the way Dan predicted his mother's death confirms it. Dan saw people who were going to die with their is faces surrounded by flies, and as his face worsened he became less visible. When Dan arrives in New England, trying to escape his alcoholism, he manages to develop the ability, even more, becoming the perfect person to accompany people to die, thereby acquiring the nickname of Doctor Sleep.
It is also a nod that Stephen King gave to the character of Dan Torrance, who as a child received the nickname of Doc, so Doctor Sleep is an extension of that nickname.
The reasons could be multiple, to make this move. The first reason is that in short, Mike Flanagan needed to create new scenes for Doctor Sleep and it was expensive and ineffective to create digitized versions of the original actors. And by the way, the mere fact of using digitized versions of Nicholson, Duvall, and Lloyd, would involve spending a lot of money on image uses, which could easily be avoided using other actors.