[o11c]

Because most real-world problems are subject to hysteresis [1], and declarative systems fail very badly at modeling history.

A very simple example:

* install a server program, which for security is run as a dedicated (newly-created) user

* run the server program, which generates logs owned by that user.

* uninstall the server program - but the user must not be deleted while the log files exist

This example is simple enough that many declarative systems don't require too much massaging to handle it, but many more complicated examples exist.

[1] https://en.wikipedia.org/wiki/Hysteresis