Um, actually, they are. They know all the arguments, Josh for instance has been aware of objective testing since the 789 days and mentions when a device also measures beyond threshold of audibility. He thus knows psychological and run-to-run predispositions can change on a dime. For him to continue to give "his thoughts" would be like me saying "yeah I know science demonstrates this, but... let,me,tell you, guys. This has to be the best thing I've ever heard in my life".
If he were being honest to a respectable degree, he would leave exclaimers about how even time of day can affect your listening experience, your mood, etc..
Let alone being sent products to review that cost thousands sometimes (which in of itself imparts a heavy bias, on top of things like price bias, even if he had to return all the products, access matters).
So yes, they are snake oil promoters, and at worst, willfully keeping themselves ignorant to concepts they should be taking upon themselves to educate themselves about if they want to do a review the justice it deserves for such a large viewership. I don't see the mutual exclusivity of being a snake oil promoter, and being ignorant. I think all three can be present in various quantities all at the same time. And the levels of these labels grows as you become more prolific and are looked upon by viewers in hopes of providing quality information. I don't take it to be the case that people get more idiotic as their fame grows, unless of course they suffer period head trauma that would allow this opposite trajectory to how a human mind usually functions.