My view is that this is not primarily about cultural changes in people's listening preferences - people aren't suddenly more interested in old music than they used to be.
Instead, I agree with the comments above that focus on changes in the industry and the economics of making money from music. Streaming promotes a background-music/party-music/infinite-shuffle kind of listening, often with little active input or song-by-song choice or oversight from the listener. And there are no conventional DJs. This means the listening experience doesn't really promote the music or cement any particular album or artist in the listener's mind. So older music has the advantage, because it is already cemented in the culture and the public imagination from years past when people encountered new music in a different way.
Similarly, as noted above, the venues for making money off of the publishing rights to back catalogues have multiplied greatly in the last 10-15 years, which again favors older music because in most cases advertisers, movie makers, video game companies, etc are looking for music that people are already familiar with, because usually the entire point is to use the cultural caché of known, popular music to promote the advertised product, the movie, the game, and so on.
Interestingly, the article says this issue is also showing up in record-store purchases, but there again I would say the above two trends are probably driving those purchasing decisions - not to mention, I would guess that middle-aged and older folks are disproportionately represented among record-store purchasers - and those older, more affluent buyers are not only probably more numerous than younger LP buyers, but they also probably buy more records per capita.