"The company's CEO said the total cost of ownership of the new mainframes is about 50% lower than that of the company's sprawling server farm."
"However, mission-critical workloads that typically run on mainframes aren't a good match for public clouds, because mainframes are far more reliable. Public clouds such as Amazon's Amazon Web Services sometimes undergo unscheduled outages, and often the system must be rebooted in order to apply security patches or upgrades. For companies that require 100% uptime, public clouds simply aren't feasible."
If you're looking at a clean room build, it might not make sense often. But if you're starting with certain situations that accumulated over decades, maybe?
I know a lot of the people I work with are gradually porting stuff off mainframe onto more modern hardware stacks, but Rome wasn't built in a day, etc etc.
100k gets you lots and lots of servers with crypto hardware.