Why hasn't the POS problem been solved yet? I'm assuming there's either some blindingly complex/simple reason because it's a large problem that frustrates a lot of people.
There's also this kind of "blood sweat and tears" attitude with a lot of food service management, and so things they see as conveniences are a sign of weakness.
There's also the fact that switching POS/ordering systems requires re-entering the entire menu and all options, and it's often management who's expected to do that.
All of these things (again, in my observations) add up to a much smaller actual market for selling such devices than one might think at first blush.
Without trying to toot our horn, it's a lot better than any of the legacy systems out there.
So no, there ins't really a reason why there isn't a solution except that nobody has made one yet (except for us and a couple of other tablet based POS systems).
It's a massive cost to upgrade, because they'd have to upgrade everything.