It's due to the stacked cache being harder to cool and not supporting as high of a voltage. So the 3D CCD clocks lower, but for some workloads it's still faster (mainly ones dealing with large buffers, like games, most compute heavy benchmarks fit in normal caches and the non 3D V-Cache variants take the win).
Interesting. I can't find any info on that. It seems that makes sense though since the 7900X is 50 TDP higher than the 7900X3D.
"Right, but my point is it's misleading to call out higher core count and the advantages of 3D stacking"
Yeah, that makes sense. I didn't realize there was a clock penalty on some of the cores with the 3D cache and that only some cores could use it.