At this point, with datacenters having been in wide production for the last 20 years, there should be plenty of 7+ year veterans.
(though yes, I have known in-house service providers that couldn't set up a new VM to save their life)
I've seen innards of very large DCs for more than a decade. At one of my first jobs at a fortune 500, I was responsible for everything from rack and stack to the command prompt. The expected turnaround time for a single physical server was 4-6 weeks until the application could be installed on it! One of the reasons was that they did not have automated DHCP/PXE provisioning. I started the process to enable it.. going through all the political, security mess, it was 9 months until it was enabled. I was gone by then.
An extreme example for sure, but if AWS revenues are growing like they are, then surely such issues are everywhere to some extent.
When it comes to in house DCs, very few companies seem to have that top talent.
For example, most companies are simply buying regular Dell/HP servers, Cisco switches/routers, slapping them in cabinets and calling it a day. They simply do not know how to take advantage of high density platforms like open compute, or of SDN. They also throw millions at software vendors like Vmware/CA, instead of building their own provisioning or CPU/RAM/Disk aggregating solutions with open source or custom tools.
If they don't know how to do it, then the theoretical savings for certain companies, of bringing things in-house simply won't materialize. And then its better to throw money at AWS if your in-house "engineers" are also breaking things 10x more often.
In a company with a badly run DC, developers very quickly latch on to cloud benefits like not having to wait for 3 days for DNS request, and 2 weeks for a VM.