I think of it like fashion. Outfits get slim/tight then the next generation comes and fits get roomy/baggy, then then next generation comes and they'll get slim/tight. There is a swaying back and forth from formal to relaxed, even in politics. Like a Boris Johnson in the UK.
I think it can just feel like "the big change" when our own generational cohort makes the break. And baby boomers have been dominating the conversation for so long, that the particular change that happened in the 60s is banged on about so much. In fact, in the article the author themselves tries to downplay the change that happened in the 90s as a change in how billboard ranked artists. I think that is actually partially just a desire to see the 60s as exceptional or legendary in a way that plays into boomer nostalgia.