One of the reasons people have been forgotten in the past is that their work was ephemeral. Now, you can go to YouTube and see Bing Crosby, Bob Hope, and Red Skelton. Even if they fall out of fashion for a while, there are always fans, and they could suddenly become well-known and popular again for a variety of reasons.
The Beatles records are still selling quite well, with many listeners among the millenials.
....And at Christmas time, the music they do, Christmas music wise are classics.