It's usually because the software accrues warts, procedures, and special cases that get baked into the company's very core. They're all different and all valuab

It's usually because the software accrues warts, procedures, and special cases that get baked into the company's very core. They're all different and all valuable. Replacing them requires someone who fundamentally understands why it's all screwed up before they can find a workable fix (Chesterton's Fence). But that's boring, awful work. It takes zillions of meetings trying to pry information out of unwilling participants who just want to do their jobs. And Reports! Acres of impenetrable reports trying to document what you found. Nah, it's more fun for consultancies to roll in and rewrite everything, and then send every department through crazy change management. Suddenly there's a showstopper that nobody noticed until now, the project is already millions of dollars over budget and years late, so it craters. A few years later another CIO does it all over again.