Software estimates also often fail to account for external factors. You may have a fairly good sense for how long some feature will take to get to code-complete

Software estimates also often fail to account for external factors. You may have a fairly good sense for how long some feature will take to get to code-complete. However, code reviews on many times are nobody’s job, so they happen whenever (and you end up with a Volunteer’s Dilemma of completing them). Then CI, linters, etc. may have various failures. Some of these may be legitimate, others may be flakiness your team has decided to ignore, or even infrastructure issues that prevent them from running at all. There’s enough X factor in external sources alone to make any estimate you provide total nonsense.