The most recent generation of IBM mainframes allow for things like hardware-assisted verification on every transaction running through the system - allowing things like credit fraud or bank fraud protections to be run with hardware assist on every transaction. It's pretty slick stuff.

IBM is still building new mainframes. IBM doesn't even build PC's any more - they sold their PC operations off to Lenovo more than a decade ago.

Financial companies also have a multi-billion$$$ investment in code they want to keep running - because it works, it's been verified by accountants, CPA's, and the like, and for them, it's cheaper to just upgrade the mainframe, run VM on it, put the old software, with old operating system, into a VM as a guest, and just keep on chugging along. It's also more secure than running Real Money on a PC-architecture system - partly for reasons of obscurity, partly because the systems, being decades old and thoroughly shaken out, have most of their bugs fixed a long time back. VM/370 preceded similar programs on x86 architectures like VMWare by, oh, 25+ years. There's lots of reasons to run a S/370 architecture with VM if you have to be able to run an old system while you shake down the new one.

Whilst shearing alpacas locally, I got to meet a guy who is the head technical guy at one of the largest credit card's transaction processing shop in Colorado. His description of their hardware made it pretty plain that mainframes aren't dead. They're just humming away in obscure buildings, that are meant to be obscure, because it's part of their security. He said that they'd tried to migrate to Oracle on Unix servers. Mainframes cost more, but they still won in terms of uptime - which, in the total cost picture, was still a big win.