@cheberly603,
Welcome!
You kind of answered your own question. Back in the late 1800s and early 1900s, they didn't have digital, count down clocks. They used a stop watch which later evolved into a large stadium (stop watch style) clock. It wasn't till the 1950s when the digital countdown clock came into existence/use in the NHL. People didn't want to do the math to figure out how much time was remaining in a football or basketball game so they started using the countdown method. The NHL adopted the countdown clock after the NBA and NFL started using it.