I think it'd really only be surprising if the Mac Pro ignored these chips when they were already available. At this point, though, the Mac Pro is shipping before Rome is available. The timing is just off. Current Xeons are faster than current Epyc's on average, so the choice today makes sense. Particularly if Apple wants to avoid NUMA in these machines. It wouldn't be unreasonable for a Mac Pro refresh in 2 years to switch to Epyc, though, if current trends continue to hold.