I said it takes years. The point is that you can do it incremental. But that typically doesn't fit with the way enterprises want things done. They want to know a beginning, a timeline and a price. Since they don't get that, they simply give up.

But it's dumb, since those systems run already and have to keep running. So they need to keep engineers around that know these systems anyway. Since maintenance work likely doesn't take up their time, they could "easily" hit two birds with one stone. The engineers have a fulltime job on the legacy system (keeping them in the loop for when an incident happens without having to pull them out of other projects then and forcing them into a context switch) and you slowly get to a modernized system.

Not doing anything doesn't improve their situation and the system doesn't get any less complex over time.