I think it's more that touchscreens are superior for certain kinds of activities, like consuming information in the form of feeds, videos, and images. Mostly because the screen is larger for the same device size. Buttons are more accurate for typing, and often (I believe, without citation) faster for typing as well, even compared to swipe systems.
One is not superior to the other over all, but each is better at certain things. The difference is that more people will pay money to maximize their user experience scrolling through feeds and watching videos, compared to typing emails.