Because none of us actually knew what RDNA2 was exactly? Don't tell me you weren't among the people who were absolutely sure RDNA2 was exclusive to 7nm EUV, because that's what 99% of people in this thread were thinking for the longest time. The common thread of thought was that the systems would most likely be 7nm, and AMD's little graphic placing '7nm' above RDNA2 at the conference just caused some of us to assert that position even if the naming change wasn't for what most logically assumed upon seeing it.
In fact prior to AMD's conference I thought BOTH systems would be RDNA1 with large amount of RDNA2 features customized to their APUs, because there were a few other posters claiming RDNA2 as a feature set standard that was node-agnostic. Which is still partly true; both APUs aren't going to be exactly like the PC RDNA2 GPU cards AMD will launch later this year.
It's only been after that conference where we got clarification directly that RDNA2's 7nm node reference in the slides was down to nomenclature, not that it is actually a 7nm process. And that's when I accepted that both systems must be on EUV for the GPUs.
And from there I've been able to look at Oberon in hindsight and deduce that it is pretty much an RNDA2 chip since it and Ariel are the two PS5 GPUs we've found data on (from AMD's own databases btw, regardless of what platform or services AMD seems to be using to store (likely copies) of the results) and E0 has a log date of December 2019, which matches up pretty well with the rumors of the then-latest PS5 devkit around some time in January.
So unless there's yet another Oberon revision with a log date of January this year that got out just in time with that recent dev kit, then by and large it means Oberon has been an RDNA2 chip since at least E0, but probably even longer than that honestly. Not hard to assume, either, if Microsoft has supposedly been further behind in dev kits overall yet had a semi-final APU shot of an obviously large APU (larger than one having a 40CU GPU at any case) right in time for CES.
Honestly I never even paid attention to the Navi10 listing in Rogame's tweets, either, but even that can be rationalized as either referring to an earlier Oberon revision, or not referencing Oberon at all, rather results for Ariel iGPU profile regression using an Ariel testlist. I was never pushing Oberon (or by relation, PS5) as an RDNA1 chip without ALSO speculating XSX was an RDNA1 chip (in fact I was speculating that even after MS's XSX info reveal that Monday a week or so back!), and this was all because of non-clarity by AMD on what RDNA2 actually entailed besides a few known features like RT, VRR and VRS.
For the longest time my thought was both systems would be on 7nm and thus RDNA1 but customizing many RDNA2 features to their APU silicon, which wasn't and probably still isn't a crazy thought to have; both Sony and MS have heavily customized their console chips in the past going even as far back as their respective first consoles.
I don't have enough time to search my older comments so you'll just have to take me at my word on this Just know there's never been any nefarious agenda with me when it's come to referencing any of the Github data or testing data from sources like Rogame, Komachi etc. when discussing PS5. I just reference that info because it's hard data, has a consistent pattern, related data (such as existence of other GPUs and chips in AMD's product line) being more or less verified of its accuracy and existence in other cards and products surfacing using chips reflecting that data and benchmarks precisely, and has a time scale that can be followed. All of which is very important to me in discussing next-gen even if some of that data ends up outdated.
It's not my only reference point in terms of sources when talking about next-gen but it's arguably the most pertinent IMHO, and there's several ways it actually lines up with several insider claims as well including Jason, Matt, Klee, Osiris, Heisenberg you name it. At least the ones that have a bit more context to them, anyhow, regarding the next-gen platforms.