Developers will discount the time they spent formulating prompts, and criticailly evaluating the results, because those activities don't feel like development.

It's like if you nag a kid into cleaning their room, and give them detailed instructions on what to do next once they begin the activity, you might underestimate the time you spent, focusing only on the actual clean up time executed by the kid.

Part of the reason may be that the interactions are not recorded. The record of development consists of deliverables like source code, bug reports and documentation. Interactions with AI are gone, just like editor keystrokes.