That's the problem. From my reading of the article, their client was, probably legitimately, concerned with the risk of a cutover to a new and unproven system.

To implement a new system the client always needs to do UAT. That's actually a drain on their resources, and if they have a working system it is far better to have incremental changes made and a regular set if bug fixes than to launch a new system, then find a raft of new bugs or unexpected changes that need to be fixed anyway.

Existing systems allow enterprises to operate effectively. New systems almost always cause unexpected disruption to a business regardless of efficiencies gained from the new system. And most IT systems are to support the objectives if the business, they aren't the actual objective if the business. A software development company can lose sight of this because it IS the objective of their business :-)