Chrome(OS) and others might use PWAs behind the scenes, so depending on how you count, maybe the numbers are much higher than I’d think?
To be clear, it's not really critical. They can do their job perfectly well using the app in any browser. But having it full screen does improve the UX quite a bit.
On my RadioSide, when the user selects to add to home screen or install as an app, it makes an icon and that's that, from the user's point of view it looks like an app, works like an app, quacks like an app, without the risks and hassle.
Most users have no idea that it's possible thus presenting them with an "install this" they already get anxiety attacks of downloading and running stuff and taking risk, I am talking about average users.