Looking around me I was convinced that most of Nike's and Adidas' sales were coming from the "fashion" side of things. People buying everyday shoes from a famous brand. The "professional" shoe was for professional athletes, football players, etc. I'd hear that a player signed with Adidas, or a runner was wearing Nike for a race, but regular people didn't go in stores for the specs, they went for the brand.
Like you say, until recently almost nobody had running shoes because running as a sport for regular people wasn't a thing. People would have some trainers that fit every sporty activity. Just because people buy more running shoes doesn't mean they buy less of the day too day shoes. Fashion and sports shoes don't replace each other. The sales of sport shoes just created a new market, they didn't cannibalize the rest of the sales. That must have been self-inflicted.
Like you say, until recently almost nobody had running shoes because running as a sport for regular people wasn't a thing. People would have some trainers that fit every sporty activity. Just because people buy more running shoes doesn't mean they buy less of the day too day shoes. Fashion and sports shoes don't replace each other. The sales of sport shoes just created a new market, they didn't cannibalize the rest of the sales. That must have been self-inflicted.