The main reason is almost certainly legacy code and integrations which are hard, risky and most of all expensive to change. No business in their right mind wou

The main reason is almost certainly legacy code and integrations which are hard, risky and most of all expensive to change. No business in their right mind would want to be on out of date, proprietary technology with hard to source skills, but the cost and effort of migration is enormous. There are scare stories of SAP migrations costing $billions and I assume a mainframe migration could be multiples of this. What would be interesting is if they let actual enlightened techies size up and run these projects, rather than giving to Accenture and the like. Maybe it wouldn’t be insurmountable then?