I would honestly argue more people know about Muddy Waters today because of the internet than 30 years ago...
That’s true, but one thing that has changed awareness of obscure music is it being used on soundtracks and commercials. Whereas movies and TV soundtracks used to be primarily orchestral scores written for that particular film or show, today collections of pop songs are much more common.
I never watched Guardians of the Galaxy, but it’s soundtrack made up of hits from the 1970s was very popular. Suddenly people were listening to songs that had been on the radio 40 years earlier, long before many of them were born.
Before that VW ad using Nick Dake’s “Pink Moon” he was just another cult musician who had died early without having commercial success. After hearing that commercial, people wanted that recording. Suddenly all his albums were in print again and his record label started digging in the tape vaults for unreleased material, tribute albums started popping up, etc. Way more of Nick’s records have been sold since that commercial than were sold while he was alive.
The impact of TV and films has always been there. From the 1930s into the 1950s, most movies had a scene where one of the actors lip-synched to a song. Sometimes popular musicians would lip synch the song. Most of the “American Songbook” material that turned into jazz standards came from movies and Broadway shows.
Bill Haley’s “Rock Around The Clock” had already been a hit in 1954 when it was used as the theme song in the 1955 movie "Blackboard Jungle" (the film was about juvenile delinquents in high school). That film’s success led to many films with silly plots about teenage rock fans, DJ Alan Freed played himself in five that were released from 1956 to 1959…”Rock Around The Clock”, “Rock Rock Rock”, "Mister Rock and Roll”, “Don't Knock The Rock” and "Go Johnny Go”. Chuck Berry appeared in three of these, but other early rockers seen lip synching on screen were Bill Haley (of course), Little Richard, Eddie Cochran, Jackie Wilson, Richie Valens, LaVern Baker, Screaming Jay Hawkins and a number of doo-wop groups.
Of course Elvis Presley had the most exposure of any rock musician in films. He starred in 31 movies between 1956 and 1969. In many of those years, two or three of his films came out. With only one exception that I know of, the rarely seen western “Charro”, all had scenes with Elvis lip synching, often in outlandish circumstances. Fifteen soundtrack albums were issued from the films, many had hit singles. These films were seen all over the world and made Elvis the best known rock performer until the Beatles arrived.
The success of “A Hard Day’s Night”, the first and best of the Beatles movies led to many other rock bands, mainly from the UK, doing their own films. Few of them were any good but they helped those acts sell more records.
From the dawn of TV until the early 1980s, “variety shows” were everywhere. The cliche of people picking up guitars after seeing the Beatles play on the Ed Sullivan Show in 1964 is based in fact. I was a 9 year old kid who had never seen a live rock and roll band even though I was listening to the Top 40 radio of the time.
There were so many of these shows and they all had music performances, often sharing the screen with comedians and in the early days acrobats, puppeteers, dancers, etc. Ed Sullivan’s show was what brought the British Invasion rock bands into living rooms here in the US. Soon most variety shows starting having rock bands on as well. While there had been local and regionally syndicated country music shows, in 1969 Hee-Haw was the first nationwide show focusing on country music. That was followed by the Johnny Cash and Glen Campbell shows. My dad was a country fan so he watched it every week and that’s where I started getting interested in country music as a teenager.
Then along came MTV, followed by the Internet. You all know the rest.