I imagine the reason we don't see as many AMDs reviews include...
a) Less manufacturer's models available.
b) Sales are 5:1
c) Many vendor's don't want detailed reviews
Most GFX card reviews consist of"
-Wording from manufacturer's press release
-A handful of Game benchmarks
-A "Gee its great" conclusion.
Vendors may not want to send samples to sites like TPU, Bitech, Guru3D who do detailed tear downs and report PCB components, PCB Cooling, temp and sound measurements because their product doesn't measure up well against the competition. I have noticed of late that certain manufacturer's and model lines are no longer being sent out. A good example is EVGA SC line.
The aforementioned sites all note the major fail that was the EVGA SC 970 whereby 1/3 the heat sink missed the GPU. We saw the fail for the 1060 - 1080 SC and FTW likes where they cheaped out and skiped the thermal pads which would have prevented the cards from going up in smoke. While it was perhaps well known that since the 5xx series, the SC line almost always used a reference PCB, it wasn't generally addressed in most reviews. So since the 9xx series, I have noticed a scarcity of reviews being done on these cards.
I notice that TPU only has the Reference Vega 56 or 64 ... I have no way of knowing why MSI and Sapphire decided to follow past practice and submit samples ... playing devil's advocate, I can imagine one reason might be that there is a general perception that AIB cards are superior to Reference cards and, if the AIB card doesn't provide that, well maybe it's best not to help that info get out there.
In short, there are various answers to your question, some obvious, some just supposition ... but I gotta think, if a card was sent to TPU, sooner lor later it's going to get published on the site.