Remote hands won't order your servers, configure your networking, install OSes/configure your PXE, and all the other tedious things running your own DC entails.
Yes, most DIY DCs are done terribly, that's to whole point - if so many people struggle with that, doesn't it make sense to just outsource it?
Absolutely agreed. That's what i used to in part do, and it's a massive effort to do everything automatically and efficiently, and it needs multiple people's time to create and maintain all the infrastructure, glue between different systems, scripts, tools. Even components as basic as DHCP suck absolutely (your options are either something from the 1990s, isc-dhcp-server, which lacks an API in any real sense, or Kea, made from the same people, which really shows), and before Tinkerbell there was literally nothing that could be used to automate such a thing at scale.
And more to my point, how many datacenters do you think are "modern"? I've only encountered one that was starting to get there (where i used to work before an acquisition by a company with arcane practices in their DCs), and having worked with hundreds of customers with "on prem" stuff, for the vast majority it's a legacy horror show.
I’m increasingly convinced that the large scale companies that don’t do bare-metal because they never learned how, and all the people advising them have never done bare metal or have done it poorly, so it’s like the blind leading the blind.. But they are leaving a 50-90% cost savings, better control over reliability, latency, data residency, etc on the table by doing so.