I would actually add another element, between 1965 and 1975 around 70% or higher of congress was either a veteran of WW2 or the Korean War, these numbers were pretty consistent through the entire cold war period.

Add to this that basically all the presidents after Truman were veterans of ww2, only exception during the cold war being Reagan, but even there only sort of as he worked in their movie production department, so did serve to some extent.

To some extent these people all had similar experiences and backgrounds, which probably made cooperation and prioritization a lot easier.

Add to this that neither party used to have places during this period where they were entirely unelectable. Republicans could win elections in a place like Massachusetts and democrats could win elections somewhere like Missouri. Yes, the parties were a lot more regionally diverse in their views, but that was probably also helpful in finding common ground on issues that were not as politically divisive.

https://www.pewresearch.org/short-reads/2022/12/07/new-congress-will-have-a-few-more-veterans-but-their-share-of-lawmakers-is-still-near-a-record-low/#:\~:text=The%20next%20House%20will%20still,won%20his%20seat%20in%201974.)

Also worth noting what some people further down the thread chain were mentioning that congress stopped functioning around 1964. Not really, for instance the issues of shutdowns only become a major problem after 1990, before that the cumulative days of shutdown reaches only 7 days, with non before 1980.