To be fair, RDNA2 as an architecture must have been finalised quite a long time ago given it's been integrated into the APUs of both consoles, usually takes a fair bit longer to make a complete APU out of an arch than the GPUs, so they must have been "holding off" somewhat on this launch, or not super rushing to get dGPUs on sale anyway, I guess possibly due to agreements with Sony and MS, maybe to build stock, maybe because of capacity, maybe all of these bits together, that bit we can only guess
And of course, AMD have been using this node for 1 month shy of 2 years now, TSMC 7nm is fairly cheap and mature all things considered, hence why it's viable for huge console chips and such.