If it is Thunderball that makes sense from a licencing perspective it's the only film that the rights are different for, hence the remake called never say never again, unless the brocolli's managed to get the rights back
From memory so apologies for any inaccuracies but the rights where not different, it was all due to a dispute between the writers of a screenplay that was supposedly copied by Fleming, leading to him writing Thunderball.
The writer and creator (might have been two individuals) who claimed it was their original work sued Fleming and his estate and won, but a stipulation in the win ment that they only won the rights to that story and it’s associated characters, events etc.
Basically they had to remake Thunderball if they wanted to make a movie, which lead to Never say never again being a carbon copy of Thunderball with a few name and location changes.
Also I am pretty sure it was finally resolved around 2012/2013, will have to Google that one to be 100%. Anyhoo I’m sure that is why they could finally use Blofeld and SPECTRE in Daniel Craig’s 4th movie of the same name, something they originally wanted to introduce in Skyfall but where legally unable too.
As for the choice, they are obviously going for classic elements and other than Bond himself the DB5 is the next most recognised Bond element yet it was only used in Goldfinger, Thunderball, Goldeneye (SEGA already did that one) and every Daniel Craig film.
Daniel Craig is abit of an a**hole and hard to negotiate with from what I hear especially when it comes to Bond, Thunderball is likely the cheaper of the two Connery entries and we all know Stern love to save a few pennies.
Geek rant over
Edited to add some comma’s, got a little carried away with the rant!