But mainframe customers are still dumping them, and they're not picking IBM: https://cloud.google.com/press-releases/2020/0121/sabre-and-...

Note that SABRE is the OG enterprise app, by most measures it was the first non-military/govt/research computer system, going live in 1960 (!) and the core still runs System/360 (which they had to migrate to, not from!).