If this software was developed in-house, the agency or owner may be able to support it. If the software was developed by an outside vendor can't be maintained by the user, the organization is stuck with it. When business requirements change, such orphan software cannot change with it. The costs of hardware and software replacement will generally be greater than a normal software upgrade from one version to another. It is easier and less risky to manage small system-change projects than large ones.
Time spent in training is time away from performing primary duties.
This is true of small or large increments of system change, but one big project and its associated time consumption is usually more disruptive and costly than two small projects in succession. These cost not only additional overtime, but also additional sick leave and staff turnover. Some county agencies are required by state and federal governments to report statistics regarding workload and expenditures. The state and federal governments intermittently change these mandates, sometimes without much advance notice. To compound this problem, state and federal authorities making these mandates tend to assume that counties have the systems resources necessary to respond to them.