While the music world was changing, the large recording companies had become more conservative, sharply disapproving of Rhythm & Blues. Until the 1950s, recorded music was only for sanctioned/approved artists, so those that liked Country or Rhythm & Blues had to listen to the radio. But the the improved recording technology democratized the music industry in large part because recording songs became very inexpensive.
In 1954, Bill Haley and the Comets did a version of "Shake Rattle and Roll" which sold over 1 million records by February 1955. Also in 1955, Chuck Berry became the first African-American to top the "white chart" at #5 with "Maybellene", and Little Richard soared up those same charts with "Tutti Fruitti". After Elvis was interviewed by Dewey Phillips on the air in Memphis, Elvis' musical career skyrocketed, first regionally, then nationally. Elvis became the star of a touring group that was managed by Colonel Tom Parker.
Presley's timing was perfect, with the crossover of Bill Haley, et al, in full swing. There was nothing parents could do about their kids listening/buying the new kind of music. Teens had more money to spend than any other previous generation of teens in US History, and the technology to play records was abundant and affordable. Elvis started to reach the stratosphere in 1955, when U.S. teens were starting to spend an incredible amount of money on the music of their choice. These teens didn't remember the Great Depression, and saving money didn't even remotely register on their horizon. A byproduct of the rising affluence was that the average middle class teen had $10+ a week ($90+ in 2015 dollars) to spend, a remarkable amount at that time.
Teens no longer depended on the family appliances, and could listen to music away from home in their cars or with transistor radios (beginning in 1957). Disc jockeys became the most trusted adults for these teens. For the first time, teens had become their own separate, defined part of U.S. culture, and Elvis was the first major beneficiary, entering millions of American homes on the sly via the radio.
By 1956, Elvis had become a national celebrity and a national issue, with his success defying imagination; "Hound Dog" sold 2 million copies, while "Don't Be Cruel" sold 3 million. Elvis was selling $75,000 worth of records each day. Elvis had appeared on Milton Berle's show twice, really cutting loose the second time, causing an uproar over the vulgarity of his act. Sullivan announced that Elvis would never be on his show . . . the Guardian of Public Morality had spoken.
Within three weeks of making that public statement, Sullivan had to change his mind after Elvis appeared on the Steve Allen Show on 1 July 1956. Allen had Elvis sing "Hound Dog" in a
tuxedo to a basset hound, and Elvis' fans hated it; the fans felt betrayed, and Elvis felt humiliated, wanting-and-needing another chance on television. Nevertheless, Allen had bested Sullivan in the ratings, and Sullivan immediately surrendered to the obvious.
After Elvis' third appearance, Sullivan sidled up to Elvis and called him a real, decent, fine boy, which was a televised surrender to the new order of things. Market economics had won, and unlike Jazz, the soon-to-be-called Rock 'n' Roll involved the masses in a visceral manner. New forces driven by technology had won, and teens didn't have to listen to their parents nearly as much anymore. Marlon Brando and Elvis were only the first of the new rebels in the world of entertainment. The common thread of those two, and their successors (e.g. James Dean), was that they projected the image of being misunderstood, especially by their parent's generation.