Many of the people who knew of Elvis' work or The Beatles' work are dead as well. But everyone in any given restaurant had heard of both of them. So they are "historically relevant" to me. 30 years from now, everyone will still he able to say they know of Taylor Swift.
You're comparing artists who grew up in an era where the transmission of information, let alone music, pales in comparison to today. Today there are endless streaming services, social media and it doesn't help that Record labels have figured out how to manipulate the teenagers who spend the $$$ on said artists with formulaic beats, lyrics, etc. Swift has the luxury of the internet to help spread her influence. Package that in good looks and regardless of talent you'll have today's pop star. If you have looks and some talent, a record company will just bombard all these services with their product. Easy to be recognized when you are on every screen, radio, streaming service, etc.
One only need turn on the local radio for one of the many sh*tty top 40 songs playing on the air. It's nothing but formulated homogenized, over produced ear worm music. Taylor Swift is very talented, but her music is a gimmick just like all the other pop crap on the radio, which is why she's so popular. She's more than capable of producing music that isn't this, but I'm guessing like Lady Gaga, and many others, a manager or someone in the business gave her a heart heart and said "You can either be a singer/player of substance who will fade into obscurity or we can turn you into a multi million dollar pop star".
Either by choice or pressure or other, she went the route of $$$$ vs substance. Can't say I blame her. Lady Gaga had the same choice, she took the $$$ . Vanessa Carlton is arguably a better singer and pianist than Lady Gaga, had the same choice, but she declined. She's an example of someone who shunned the pop star route, and thus became a 1 hit wonder. (You can actually find an article of Carlton talking about the pressure to become a pop star and refusing to do it after A Thousand Miles won a Grammy).
You simply can't compare success of today vs the 50's, 60's, or 70's. The game was still in development back then, and you had to have talent, looks were optional. Today, talent is optional, looks almost always required.