I think I’ve made this comment before, but there really are some jobs that monolithic big iron does better, particularly in banking where you need guaranteed exactly-once delivery scaled massively to support transaction processing, where re-creating the system with a modern architecture would need multiple times the infrastructure and maintenance. That combined with existing COBOL/Natural codebases that work pretty reliably and are regulator approved gives mainframes an element of inertia that I suspect will outlive even me.