I use Roll20, a popular web app for playing tabletop games with others over the internet. It doesn't work in Firefox or Safari; it's the only reason I keep Chromium on my machine.
Roll20 is also such a niche thing already it's not really a fair example. People who want to use roll20 will use another browser because they want to play dnd with their friends. Most stores don't have that social aspect.
It takes someone who really cares about these issues to bother switching back and forth between two different browsers because you want to use a non-Chromium for most things but have to use Chromium for a couple of things. The vast majority would just say "well, whatever" and switch completely.