What feature did radio in the 1920s offer that other inventions did not offer?

When the first radio broadcast was heard in 1920, from the radio station KDKA,  people were surprised because they could hear voices and music in real time which was very futuristic, and no other invention had that feature. Even though most of the radio listeners could not hear that first broadcast because their radio receivers were not that sophisticated, the radio craze had began and a mass production started to satisfy the demand.

More than 60% of American families between 1923 and 1930 bought radios. Entire families will gather next to the radios to hear music and news. It was a form of entertainment at that time. The number of radio stations increased as more radios were purchased. As time went by the radio programs got more sophisticated and creative.

Radio was free for all at that time, but after some complaining to the government from broadcasting companies and radio listeners  for some intervention, the government slowly responded by passing laws to somehow govern the radio.  

The Crystal Radios were the most popular at that time, so they were manufactured the most. They were very easy to build and many popular magazines at the time encourage people to build their own radios.

b) race riots in several cities

the main reason that the constitution did not proclaim all men to be free and equal is because of the issue of slavery.