Right now we have 3 sysadmins for our own DC, and they can’t keep up with all the maintenance (upgrades on infra are the worst. Software quality on switches/SANs/appliances is terrifying. And those are better than quality of Server management, BIOS, etc. Even VMware has caused lots of pain with patches and upgrades in recent years.
If you don’t ever patch/upgrade to fix all the security vulnerabilities that exist at the infrastructure layer maybe “do it yourself” is cheaper. But that doesn’t fly in the banking industry.
We’re half-in the cloud and moving more there just to keep our head above water. We’re spending way less on cloud services than the $500K/year it would cost to double our infrastructure staff and keep it all in house.