The thing is that most people, me included, don't want to spend ages researching, they want to quickly search and find a hotel at an acceptable price under a trusted brand where they know what they're getting (actually a marketing slogan for PI, it's that powerful a marketing tool). Thus BW doesn't work. It's not like the days when you'd book through a knowledgeable travel agent who would make you a recommendation having done the legwork for you.
If I book a PI I - as the ad says - know what I'm getting, and that's what I want in a hotel. I don't want a surprise when I arrive tired at 11pm on a Friday evening, I want a good quality room the same as every other time I've stayed there.
BW are either going to need to up their standards to reach this consistency* and boot others out, or probably wither on the vine as people are put off by the bad apples.
* An example might be Ibis Styles, which I believe is franchised and the hotels have their own quirks, but the fundamental standards are consistent.