I know that when I don’t floss, my gums will bleed sometimes during brushing and/or they’ll get inflamed. When I do floss regularly, absolutely no issue with bleeding or inflammation.
It’s so clear to me that I can’t imagine what the difference is between my anecdata and whatever actual data is coming from these studies.
So this doesn't necessarily mean that flossing doesn't work. It may just mean that dentists are already making money hand over fist and don't care enough to do good studies and validate that.
BTW what was specifically looked at was whether unsupervised flossing works. So another possibility is that flossing properly works but a lot of people do it ineffectively.
All things you would want a conscientious, science-based ADA to care about
Do they bleed during flossing though? I used to get bleeding gums after brushing teeth, but switching to a softer toothbrush stopped it. Flossing, at the start, does cause my gums to bleed though.
After that, I never bleed during flossing. And I make sure to get it up between the gum and each tooth, so there’s a decent (but appropriate) amount of floss/gum friction.
My dental hygienist knows when I have been flossing and when I haven't.
If they start bleeding again it's a sign I've not been doing a good job staying on top of keeping them healthy.