From the late 50s through to the late 70s, headphones were big, bulky, heavy things. The prevailing design theory was that for the user to get maximum fidelity out of them, the had to completely seal in the ear. And headphone use took off, especially for people who liked albums (such as Pink Floyd’s Dark Side of the Moon) that seem made for headphone listening.
Many different speaker technologies were used: dynamic drivers, the more expensive electrostatic technology, electret-based headphones, Heil Air Motion, magnetostriction, and a few others.
But the biggest breakthrough came in 1979 when Sony introduced the Sony Walkman. They were small, very lightweight, and sounded surprisingly good. They also made walking around in public wearing headphones publicly acceptable.