What about the fact that Bitcoiners still tend to use fiat over Bitcoin, even when they're patronizing a business which accepts Bitcoin? Kinda makes it a tough sell to the next merchant who'd prefer not to go through the effort of setting up a whole new point-of-sale system only for people to not use it.

The number one reason merchants aren't adopting Bitcoin is because Bitcoiners are not demanding it. No one is boycotting business who only accept fiat. Not only are Bitcoiners generally not demanding it, they seem to generally not care at all. So, of course businesses don't care either.