In this day and age of modern first world America, the only people who take long walks on pavement are the homeless.
Boom, obesity epidemic. Walking is alive and well in most European cities which are even remotely walkable (which is most of them). I don't see people doing it in hiking boots, that'd be ridiculous. There are different shoes with different purposes and shoes which match different clothes aesthetically because style is a thing.
I mean, I understand that if you're going on a bike tour and you want to be clipped in and you don't want to bring any extra shoes, a touring type shoe with MTB cleats makes sense. For people who have other use scenarios, it just doesn't. When commuting being clipped in offers no objective benefit, and the disadvantage is that you're stuck with some sort of bike shoes, which aren't as nice to walk in, and might not go with the rest of your outfit. On the other hand, for people who're going to race, the dedicated road shoes are lighter, don't have excess stuff on them, and are stiff yet comfortable.
Sure, if I was limited to only one bike and only one pair of shoes, I can see your point, the touring style clipless shoe is an acceptable compromise, but I'm not.