I was surprised to see how few mainframes Big Tech companies that handle a huge amount of transactions (Netflix, meta, google,…) use relative to legacy industries (banking, retail, insurance,…)
This makes me suspect that the real reason why mainframes continue to exist are due to industry inertia, vendor lock-in or even legacy code rather than any performance/cost reasons.
There is a discussion on Hacker News, but feel free to comment here as well.
Also, just up and switching architectures, support models, and skillets needed within a team is a big hurdle to get over and is typically only done when companies have to. If it ain’t broke and the alternative means a massive shift in priorities and higher costs, why ditch the AS400?