Sadly, academics have the incentives to publish papers in prestigious journals that make them sound smart and not to find a simple cure. Likewise, the free market does not have the incentive to easily and cheaply cure people but to maximze profits. Hence, so much research is absolutely abysmal, wrong, misleading and harmful. Sadly the human mind is constructed in such a way that we self-deceive to gain advantages. That is why there is no need for a conspiracy but just the wrong kind of incentive structure.
That said, with respect with Seyfried's work, I urge you to give something like https://sciencebasedmedicine.org/ketogenic-diets-for-cancer-... a read. Go ahead and skip all of the bits about his chosen associations and focus on just the science parts if you would like. I think you'll find that quite a lot of research as been done on cancer metabolism, and that Seyfriend's work at best can be considered incomplete.
If you find the blog's arguments about lack of clinical trial data to be circular (I guess they kind of are), I don't have any answers for you now, but I suggest you keep on eye out for this guy: https://clinicaltrials.gov/ct2/show/study/NCT01754350
This is one of the studies in early stages that the blog links to (it's been a few years). They just wrapped up the study a few months ago, and hopefully there will be results posted soon. You can also search for that study number (NCT01754350) or study name (ERGO2) for papers when they do come out (again, expect at least a few more months).