Inertia. You have a ton of one-off specialized programs running batch operations, settling transactions, extracting reports, and generating output that will be

Inertia. You have a ton of one-off specialized programs running batch operations, settling transactions, extracting reports, and generating output that will be the input of a slew of other similar applications. All of that is densely packed business logic with very little other stuff. It'd be painstaking to convert to more modern paradigm, without dropping a single feature on the floor. Convert all the existing data and shim all the interfaces as you convert piece by piece. Importantly, the whole effort has no intrinsic business value, is unbounded in scope, risky and tends to paralyze the kind of on-going small maintenance that kept the system current with changes in practice, accounting rules, tax law, HR processes, etc. Finally, Gary and Sue who were the last ones who actually knew all the pieces of the stacks and how they fit retired in '97 and '03.