Let us imagine you looked at 100 papers, and you could tell 99 of them had severe problems, and one looked OK. That information would make you suspicious that the one paper also had severe problems, but that you just didn’t detect the problems.
From article: “We’ve gone from 29 studies to 11, getting rid of 18 along the way. For the record, we eliminated 2/19 for fraud, 1/19 for severe preregistration violations, 10 for methodological problems, and 6 because Dr. Meyerowitz-Katz was suspicious of them.”