I understand why Apple decided to ship some YouTube blogger an evaluation system; Visibility. What I find puzzling is why only to YouTube bloggers? We keep hearing that "Unless you're a professional, high end, professional user this thing is not for you". I can't imagine these three individual YouTube bloggers viewers consist of many "professional, high end" users which are the alleged target market for the 2019 Mac Pro.
Your causality here is way off. Youtube blogger talking about anything remotely interesting because that is how they get paid. More juicy 'tidbit' , the more video views , the more ad views .... all lead to bigger paycheck at the end of the month.
Apple giving these folks loaners ( for a month or so or even deep discount try-and-pay-later systems ) is primarily just buying advertising. It isn't a coincidence that all of these folks videos dropped within an hour of the launch. They were part of the "guerrilla" marketing campaign. ( freedom fighter bankrolled by deep pocketed government in the shadows. )
Apple probably has given early access to other traditional media folks. However, those folks day job is not bragging on YouTube about their NDA project they are working on. Those folks will probably more so have casual conversations with friends on the "down low" about general characteristics , Also Apple has probably more so given it to folks in that realm who are going to buy Mac Pros in quantity directly. So not "advertising" to random folks who might buy. It is folks who say "if mac pro passes benchmarks we'll buy XX of them. So can we have one to benchmark with early? " If that is an instant > $1.5M payday for Apple the answer is probably different than random Joe who wants to buy one.
As far as I can tell, at least at the time I made my original statement, no technical publication appears to have received an evaluation unit.
The gamer focused Tech porn press. ... why would they be eager to give them one. Especially the ones who are primarily interesting in "got it first , here is the review of these 6 Windows games and geekbench scores and PCMark scores" ones The ones that do "deep dive" reviews ( Anadtech and some ArsTechnica ) aren't day one ( or 2-3 ) reviews. Anandtech has gotten slower of late than what they used to do.
Even the reviews that do more workstation type ones often also weave into the mix CAD apps that may not be present on macOS either.
You'll probably see stuff like this bubble out over the next couple of weeks.
https://9to5mac.com/2019/12/12/music-producers-tes-mac-pro/
That isn't really all that good if look closely because it boils down to " it was overkill for what we're doing". There are some audio folks where this won't be overkill, but lots of "overkill" stories is a dual edged sword due to the high base price of the system.
I would think Apple would have provided a few to publications which focus on the intended market. I'm sure we'll start seeing reviews from such publications but I get the impression it will be because they purchased one to evaluate and were not provided one by Apple.
Even the general gross area publications are broader targeted than this system. Apple actually doesn't need a publicity bump right now anyway. The delivery date for the Mac Pro just slide out another day to December 31st earliest now. If Apple can't meet demand, why divert one to publications? To do what raise demand even higher that they can't meet?
Apple can line up a review later for when they probably will need a demand bump. The current story is more than several folks will have by Monday.
https://www.macrumors.com/2019/12/12/mac-pro-orders-begin-shipping/
There will be dozens of folks chirping about these by next Tuesday on social distribution media sites.
The notion that a few key publications are the key to getting the marketing message out is antiquated.