Up until about the 1950s, one can see instances of social dance (especially ballroom) dominating the social scene. This includes instances such as the tennis court scene with Humphrey Bogart and Audrey Hepburn in Sabrina, several Astaire/Rogers films, and even Peggy and Steve speak of going dancing in Captain America: The First Avenger. Formal social dancing dates back to the Medieval and Renaissance periods, and have included everything from country reels to formal line dancing (as seen in film adaptations of Regency-era novels, such as those of Jane Austen) and ballroom dances such as the waltz or the more modern Charleston and Latin American pair dances.
These dances remain popular to this day in Central and South America, where parties and large social gatherings will include everyone dancing salsa, merengue, and (more recently) bachata. Yet in the United States, this style of dancing (read: "ballroom," which encompasses what were then casual or country dances) has largely fallen out of favor.
My question is this: When did such activities fall out of mode in the United States? And, furthermore, why did they largely disappear from the mainstream?
NB: I am aware of specific instances -- weddings, prom, quinceañera, cotillion, bar mitzvahs, etc. -- where such dances are still performed as part of the social norm. However, these events are rare. The average US dinner party, for example, is unlikely to include pairs dancing at any point in the evening, where at one point the living room would have been cleared of furniture and swing or jazz music played.