In my country, 30-40 years back, people who needed a watch were those ones who travel regularly. And travel was mostly using public transport, trains and planes. Most or all of it operated using a 24h time. That button was very useful. Compare that to the mute/silence/DND physical button in iPhones today.

Also people who worked in confined spaces who wouldn’t know if it was day or night outside after a days job. My father who worked in an oil rig in Abu Dhabi used one. He gifted me one.

This was 1998.