Take a look at these two metrics:
https://uma.googleplex.com/p/chrome/histograms/?endDate=20170723&dayCount=1&histograms=AppBanners.InstallableStatusCode%2CWebapp.InstallabilityCheckStatus.MenuItemAddToHomescreen&fixupData=true&showMax=true&filters=platform%2Ceq%2CA%2Cchannel%2Ceq%2C3%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial

The former is appbanner but it still paints a picture of installability of the web.
The second is more direct - regardless of completion state (i.e. whether it finishes in time), 95% of the time, it's not a PWA. I think it pretty clearly explains this.

Closing this out as per the second histogram, feel free to re-open if you think that's not an adequate explanation.