[rtempaccount1]

In many cases (e.g. banks) these systems have been running for decades, they're often badly documented and have had a lot of fixes applied for issues that arise.

Re-writing that, is going to be a nightmare, as you've got no spec. to work from and mistakes may not show up immediately (think monthly or annual payment processes)

It's a very high risk endevour with little immediate reward for the team doing it. If it goes perfectly, no-one notices, if it goes badly it could seriously impact your whole company.

[Twisell]

Same logic apply to climate change issues.

There is little immediate reward so let this dumpster fire explode on our kids...

It doesn't necessarily mean that it's a good logic. We desperately need more long term thinking.

[analognoise]

Counterpoint: a system that runs for 20, 30, 40 years without any serious downtime is the definition of long term thinking.

[rtempaccount1]

except of course where the system is ossified and you can no longer make changes for fear of affecting that lack of downtime.

In the organizations I've seen with mainframes, what happened was a panoply of supporting systems sprung up where new requirements existed as everyone was afraid of making significant changes to the mainframe environment.