When the Indiana Jones Adventure was introduced and the Jungle Cruise was re-routed and given a new boathouse to accommodate the attraction and the increased crowds in the area, show writers took an opportunity to rethink the attraction's tone and tried to further develop the setting. Wanting the stories of the Cruise and Indiana Jones to interconnect and trying to improve immersion, fourth wall jokes were banned to focus on putting people into a 1938 exploration setting. This was also around the time they introduced that awesome jazz and swing music loop that has become almost inseparable from Adventureland ever since.
A newly rewritten Cast Member manual, the Skipper Survival Guide, was developed to try and get skippers into a mindset of being in a jungle in 1938 with "1938 Current Events" listings, an animal guide in the form of an expedition journal, and character archetype prompts to encourage Skippers to try and make the show more of their own. But what we're focusing on now is the backstory of the Jungle Navigation Company and the old colonial boathouse they call home. Later Jungle Cruise projects such as the Skipper Canteen have changed some of the details, but this is where most of the notion of asking where the Jungle Cruise came from started.
