It isn't the studies, it's the industries behind the studies. Livestock is big business in the US and Canada, and have powerful lobbies and influence school programs very heavily. Cow's milk is practically devoid of nutrition (short of protein, which virtually ALL of us are already well in excess of), and there are plenty of other common foods that provide the same nutrients in higher amounts, and without the 'baggage' (like saturated fat, hormones, fecal matter, blood, pus, etc). Milk is credited with having iodine for example - fresh milk straight from a cow doesn't have much iodine, it's in the milk because they use iodine to disinfect the machinery. They may as well brag about there being soap in it as well. Vitamin D? It's an additive, an ingredient they add.
There are some interesting books that cover the history of the industry, Cash Cow and Got Milked? are two specifically on dairy, and reveal how cow's milk was lobbied into our fridges, and science and nutrition really had little to do with it. The milk industry has their inane 'Got Milk' campaign, and were willing to provide 'nutritional' information to schools, so long as it helped sell their products. (No human should be consuming ANY animal milk past being weaned, let alone the singularly bizarre act of consuming the milk from ANOTHER species! Give up ALL dairy for a week, then dig into a cheese pizza - you'll really start to see how ill equipped our bodies are at digesting dairy. Most people are just used to feeling a certain way, and don't realize the negative impact it has on how they feel since they've never considered living without it.)
Do some research into the 'four food groups' - why on earth are meat and dairy fully 1/2? Study after study after study after study shows that the more animal products you consume (almost always at the cost of reducing plant-based foods), the more diseases you're likely to inflict on yourself. Yet we get the impression that they ought to be at least fully half our diet. Going further back in time before this influence, there were 8, 12 or more food groups - back when dieticians called the shots, and not industry.
Plant-based food lobbies have much less sway. Just look at the wacky story of Hampton Creek, and the collusion between the egg industry and government agencies because their 'mayo didn't have eggs in it'. Oh, the horror. Unilever (Hellman's) was a part of this as well, and after losing stuck their own eggless vegan mayo on shelves. (Shows how critical eggs are to mayo.)
I could go on, but look at where the studies come from before what the studies say, and it becomes clear why we hear what we hear. These trends (high fat, high protein, gluten-free, paleo) come about because there are industries making profits with products and books to sell, and people desperate for an answer to their health issues. Ever ask why they almost all all focus on increasing animal-based foods?
Want to be healthier? Start where there's less money to be made: eat plants. Fruits, veggies, legumes, whole grains, nuts and seeds. Center your diet around these, and chances are you'll find yourself feeling better and see your health improve. Simply put: if you see a commercial for it, chances are you're better off not eating it.