Are the updates easy to apply? Plenty of software is incredibly hard to update. Take postgres for instance, you need to take take the whole database down or come up with a complicated replication based upgraded strategy (which it doesn't "just do" out of the box)

Restarting software can be pretty problematic if it's used in a high volume context unless it supports some form of high availability natively.

On top of that, plenty of software has poor backwards compatibility (usually not intentionally) which means a significant amount of testing is required to make sure the update didn't introduce a regression (even for minor version and patch upgrades).