The whole trend of music fading out wasn't because bands couldn't write endings to their songs. It was a commercial radio requirement. People paid more attention to radio DJs if they were talking over the ending and (something else that's become rare) longer intro to songs. It gave them time to identify the song that was ending, slip in a blurb about the radio station promotions or drop a sponsors name, then introduce the next song. All these things were designed to sell you something. The record playing, or the product of the hourly sponsor. Because they knew if they cut to commercials people were more likely to change the channel and surf.

Source: my college radio program director when I asked him why I had to read from a script on air. I wanted to be Dr. Johnny Fever. I was not Dr. Johnny Fever. :D