"Remember, AMD released an 8 core desktop CPU in 2012"
I'm assuming you are referring to the epic failure that Bulldozer was. Although it indeed had 8 full physical integer cores on the chip, there were only 4 FPUs, so it was not a true 8 core cpu, although obviously physically more than Intel's "8 thread" cpus which were 4 full cores+HT.
And Intel didn't feel really threatened by the FX 8 cores because only under ideal circumstances in which all 8 cores were saturated would it beat Intel's 4+4 solution. While sucking down a ton of juice, too. Take it from a previous owner of both an FX-8150 and 9590 (<---what was I thinking?). Most of the time, Intel's significantly higher IPC won out because 'real world performance' software in 2012 couldn't saturate 8 cores consistently.
Ryzen, OTOH is at least very close to the single thread and IPC performance of Intel's mainstream parts, while also being pretty energy efficient, to cause them concern.