To wit, the writers agreed to compress the timeline of the actual road trip, which took place over the course of a year — from 1962 to 1963 and the death of John F. Kennedy. “We had it [the assassination] in the first draft, at the end,” Farrelly recalled. “But suddenly it changed everything. It wasn’t about these two guys anymore. By putting in such a huge part of American history, it kind of altered the chemistry.”
Source: latimes.com – Los Angeles Times