Just a guess, but film studios have multiple projects up for consideration all the time. There could be any number of reasons they didn't follow through.
Budget, timing, number of other irons in the fire, maybe they just came to the conclusion this didn't have the revenue potential for the company.
Could you provide a bit more specific detail? Someone might have some actual knowledge about a particular project
They approached the BBC in June 1964 and in the 70s. Supposedly, the second time fell through because there wasn't enough money for the project but no one can tell me what happened with the first one.
IMHO Dr. Who could certainly have been a franchise worth considering. Disney "nailed it" on a number of occasions (i.e. Mary Poppins) but this may have just been something they didn't see the potential for. A Disney project in this century must have potential for merchandising and other synergy. Things were a bit less complex in the 60's . I wonder if you'd find more details in any of the Disney literature out there? There was a book focusing on the live action Disney movies. Maybe there's something in there?
I'd guess they are books on the history of Dr. Who where it might have been mentioned, but you'd probably know more about that than I do.