YouTube Reviews

I'm pretty sure I've seen reviews for McIntosh, Marantz and NAD. What you rarely see is reviews for boutique items. A lot of reviewers are sent items from the companies that can afford to do so. Some get to keep the items, some don't. 

Yes, you're missing something. If you go to YouTube and do a search of McIntosh, Marantz, or NAD, there are loads of videos up for all of them. 

well, it seems to me that many of these guys have some area of hifi they focus on and rarely stray from.

the hifi world hasnt paid any attention to marantz since the end of the 22 and 23 series, so count that out as, with exception, its just not relevant. NAD isnt really part of the current landscape, neither; its modern counterpart, schiit, very much is, and schiit gets reviewed all day long. 

here are some mcintosh c2200 reviews 
https://www.youtube.com/results?search_query=mcintosh+c2200 

you see plenty of reviews for boutique/small scale hifi  manufacturred items. like so many things, if youre not lookin you probably wont find what youre not lookin for. 
 

All three have been reviewed.  Just do a search.