Launching is what allows to work out the BIOS bugs, CPU bugs, microcode tweaks, OS scheduler tweaks, compiler bugs, at least in a good part. If anything, motherboard vendors gets "final" (as in version 1.0.0 of sorts) CPU silicon and a reason to do things other that from their good hearts.
What makes me think that is especially that they have the server CPU/platform coming after ; we've seen for years how Intel launches consumer CPU first, server CPU after that, though there it will be the same die, modulo a spin or stepping perhaps and microcode or firmware fixes/updates.
The sooner ugly stuff is fixed the better (like that bug where Windows 3.1 applications will crash among other things, we could say, who gives a crap, but somewhere there may be companies deploying Windows 10 32bit VDI to run some ugly leftover things from Windows 3.11 for workgroups days, or something weirder still)
In a way, deploying on beige tower desktop first does not entirely fit with that but it's very decent for mindshare, adoption and proofing it with a lot of hardware and software diversity ; there's been "Zen+" then on roadmap for a while that goes into low power mobile first like Intel did with Broadwell, Skylake and so on.