There is currently a lot of speculation going round that the new 3xxx series chips are at the clocks they are for a couple of reasons.
1) To enable backwards comparability with the older X370 / B350 series motherboards, as AMD had promised this would be the case and to avoid lawsuits of people blowing up their rigs by plopping in some highly clocked core count chip and burning down their house when the VRM's etc fail lol.
2) The CPU Clocks etc dont align with what should be expected from the node shrink, this reinforces the point above that the chips have been clocked conservatively for compatability with older chipsets.
3) This leads into the newer X570 series of motherboards all seemingly over engineered, because the chips have OC headroom that these motherboards will be able to exploit fully, with rumors of 5ghz single core being actually realistic, and many thinking 4.5-4.7ghz all Core OC being a real possibility on one of these motherboards.
Seems kinda plausible i guess, in reality we wont know the truth until official reviews are released, but it does kind of make sense that these chips dont seem to be clocked as high as you would expect on the node that was used, TSMC High Performance, they are barely better than the 12nm LP node Zen+ was on.
So if it turns out to be true, that indeed they have been clocked conservativly to enable compatability with older motherboards, AMD could be onto a winner, as could the motherboard manufacturers, as soon as benchmarks release for the chip on the old and new platforms, to show the newer platform pushing the chip a lot further, people will be selling motherboards to ugpade! But it also allows the casual non OC users to get in on the act with more reasonable clocks on older motherboards.
Again there is still lack of info on PBO, XFR etc.. maybe this was intentional, due to the difference in what the chips can potentially achieve on the various motherboard versions? its all speculation but it does get you thinking. Coupled with the fact the vendors have seriously gone all in on X570, something tells me this may actually have some remnants of truth in it.