First, mass media is not qualified to analyse diet studies, journalists are not nutrition scientists. No one is analyzing studies for red flags before publication.
Second is cultural bias. We love to hear good things about our bad habits. Legions of people, for example, love to see studies that say moderate consumption of alcohol is a good thing. Including many doctors. I'm not taking a position here on whether alcohol consumption is good or not good, I'm simply pointing out that bias is cultural, and pervasive. And people who enjoy alcohol are going to be happy and relieved to see a study that says "what you're doing is good". If that study happens to be conflicted (paid for by an alcohol industry group) that "little problem" somehow never makes it into popular media reports.
Third, studies cost money. Who can typically afford to fund studies? Industry groups...who can then also afford media blitz campaigns to get the "studies" before the public.
Forth, studies are complex and difficult to design and run. "Getting it right" is a narrow set of conditions, getting it wrong is everything else. Deliberate corruption of studies is not difficult, and hugely tempting to industries generating outsized profit on questionable products.
Does any of this make you look toward the flurry of studies saying "butter is back", "cholesterol doesn't matter", "saturated fats are good" with a slightly different perspective?
The Mediterranean Diet Study of 2013 made a huge media splash, and it's recently been retracted. Here's is Dr Pam Popper, who is qualified to analyse diet studies, with an explanation as to why.