Maintenance costs
Complexity in any system, just like more stuff, has ongoing costs. The cost of maintenance.
In most cases, if the cost of adding the complexity plus the ongoing maintenance costs is not outweighed by ongoing benefits through the value that it brings, then simple is better.
Before we plan to implement any change to a system or our life that adds complexity we should heavily scrutinise it, or test it if possible at a small scale before fully deploying the change.