Do you have proof of this? I was under the impression that The New 52 brought a big boost to DC's numbers.
the new 52 was a temporary boost, within a year or two their comic numbers were lower than they were before the new 52 reboot happened, from what I remember of several articles that the time. Remember, DC Rebirth was not popular with Didio or his ilk, it was done to try to bring back the people who stopped reading The New 52.
As for bad reviews, I'm not Google. it's easier to find bad reviews of New 52 books online than it is to find sand in the Sahara. Red Hood and the Outlaws was called out for being both shit and unbelievably sexist, no one on earth give a shit about stuff like Voodoo or grifter, etc. even the stuff they got slightly better reviewed was forgotten pretty quickly. No one gives a shit about the New 52 Superman books, for example.
Outside of Snyder's Batman, even the stuff that didn't get the worst reviews was not very popular in retrospect. No one's going back to Geoff Johns Justice League or even grant Morrison's Action Comics. Green Lantern books also started doing pretty badly when they made emotion and willpower a limited resource, and in general the new 52 stuff was going way down hill even from where it been which is why rebirth happened. But because the people in charge didn't want to do rebirth, they almost immediately started undermining it which lead DC to where it is today.
As for proof of Dan Didio and others sabotaging rebirth, just look at what happened with Dick Grayson and Wally West, two characters that Dan didio infamously hated and was always trying to get rid of. thinking of stuff like heroes in crisis, which was badly reviewed by most people and was one of the absolute worst things ever, and also acted as a way to basically get rid of Wally West.
When it comes to Frank Miller, you're defending them employing a guy who once wrote a several hundred page comic that's entire concept was Frank Miller ranting about how much he hates Muslim people, not to mention all the horrific misogyny (and just shit quality) of stuff like all star Batman. other people have gotten boycotted for shit like that, Marvel hasn't worked with Frank Miller in a long time, and DC working with him is always been an embarrassment of recent times.