Tons of reasons, but the main one is that cache is shared mutable state, pretending not to be. It has all of the ugly attributes of global variables, especially where knowledge transfer and reliability are concerned.
In a read-mostly environment you can often more easily afford to update the state all at once. It’s clear what the effects are because they happen sequentially. The cost of an update isn’t fanned out and obscured across the codebase, where or your team can delude yourself of the true system cost of a suspect feature.
