Whether they like to admit it or not, Pixar has been absorbed by the Disney Corporation, a company which for years has suffered from advanced sequel syndrome -- a.k.a. sequelitis, cloneitis, quick buck syndrome and marketeering mange; all names for a corporate hardening of the creative arteries, narrowing of long term vision and loss of out-of-the-box thinking, accompanied by increasing innovation impotence. It is no surprise that Pixar, along with their (and Disney's) chief animation executive and top story man, are showing the symptoms of having contracted the same disease.
There are dozens of reasons for Disney to say no to 20,000 Leagues Under the Sea -- all of them reasons that deny what Disney was and define what Disney is.
/\ This... Unfortunately sequel syndrome has a symptom that prevents hearing, seeing, or believing that the disease is a problem.