The #1 reason by far for buying a mainframe is that you already have mainframe-based applications that you need to keep running. I’m not sure what kind of orgs

The #1 reason by far for buying a mainframe is that you already have mainframe-based applications that you need to keep running. I’m not sure what kind of orgs (if any) are buying mainframes today as new customers, but I imagine it would have to be a use case something like… a niche scaling challenge, or an outsourcing arrangement where the relationship with IBM is not just vendor lock-in but is some kind of partnership, or you have specialist compliance requirements, or contractual service level obligations, or you need to provide absolute guarantees about the performance/availability/security of the whole stack from hardware up. Some organizations will pay $$$$$$$ to have one ass to kick rather than herd multiple vendors.