Daniel Craig discussed this to an extent with ComingSoon.net. He was asked about John Gardner, who is the most prolific of the post-Fleming Bond writers, having written sixteen novels between 1979 and 1996:
CS: Have they decided not to adapt any of the John Gardner’s novels?
Craig: I don’t think they ever would, because they don’t own them. I
don’t know what the deal is with that. We’re taking the original idea.
The funny thing is if you read Fleming’s (novels), which I try to plow
through occasionally, there’s an awful lot of story lines that have
never been used because obviously the films are based on the books.
There are still ideas that we can sort of pluck from.
This seems to be confirmed on the wiki of Ian Fleming Publications, who own the copyright to Bond as a novel character. This can be compared to EON who appear to hold the copyright to Bond as a film character.
Following this logic, it would be costly for EON to purchase the rights to any of the continuation novels.
This doesn't mean they haven't borrowed content from the novels before. This has been discussed over at the MI6 Community, with one poster noting similarities between the License Renewed novel and Bond films:
Licence Renewed: James Bond gets his first glimpse of villain
industrialist Anton Murik at England’s famous Ascot racetrack.
to a Kill (1985): James Bond gets his fist glimpse of villain
industrialist Max Zorin at England’s famous Ascot racetrack.
Licence Renewed: Bond poses as a weekend party guest at Murik’s large
country estate in Scotland.
A View to a Kill (1985): Bond poses as a
weekend party guest at Zorin’s large country estate in France.
Licence Renewed: Bond’s SAAB ejects tear gas from its vents when
surrounded by henchmen.
Tomorrow Never Dies (1997): Bond’s BMW ejects
tear gas from its vents when surrounded by henchmen.
Licence Renewed: Bond fights henchman Caber in the cargo hold of
C-130 over Spain in the book’s climax.
The Living Daylights (1987):
Bond fights henchman Necros in the cargo hold of C-130 over
Afghanistan in the film’s climax.
There are plenty more examples of these similarities over there.
Another factor to consider with regards to adapting parts from the continuation novels is the fact EON have always put so much original content into the films anyway. The Bond novels written by Fleming are very different to the films that were released, as Fleming wrote within the technological constraints of the time (so Moonraker does not take place on the Moon, for example) and made his "Bond" protagonist much more realistic (meaning he fails quite often, can't take three guys on in a gun fight etc).
Given EON disregarded so much of the original novels, it seems likely they could/would do something similar with the continuation novels. So not only would they have to pay to adapt the novels, they'd likely not use large portions of the novels, making it even more of an unnecessary cost.
Finally, the scripts for Bond films aren't too difficult to come up with. They tend to follow set patterns, with the gorgeous woman, the slick lines, a few car chases, etc. Given this, there doesn't appear to be a shortage of scripts or ideas for EON to use in creating the films.
So in summary, there doesn't appear to be any desire to turn any of the continuation novels into films, probably because EON don't own the rights to them and it would be costly - but that doesn't mean they haven't borrowed elements from the novels for use in some of the modern films.