[sodapopcan]

One sitting is a lot for a project you've forgotten about, lost context on, and are no longer excited by, especially assuming you have a lot of other stuff going on in your life. And then ya, everything else you said. And there are no tests.

[bombcar]

This is it entirely - imagine suddenly being asked to clean and organize a house you haven’t lived in for ten years. It may take you a day just to get back up to speed on the code.

(Interestingly enough Knuth praised literate programming for TeX as the reason he could get back in and fix bugs after an almost ten year hiatus - where parts of the code he had not looked at in 40 years.)

[seabass-labrax]

Some professional cleaners do indeed do their job on properties they might never have seen before; maybe the programming equivalent is the external consultant who is expected to quickly identify bugs in unfamiliar codebases.