The difference is that writers and mathematicians aren't typically expected to stand up every morning and explain to their colleagues and a manager who never did their job what they did yesterday, what they will do today, and what their roadblocks are. They're given a task and allowed to work for days, weeks, even months, with little or no interruption and largely self-guided.

They're also not typically creating things directly that provide as much business value as developers are.

You can interpret Hemingway’s writing process such that he really could tell you what he did yesterday and what he’s going to do today.

Not that I’m particularly fond of this current incantation of Agile.

They also arent creating output that has to be simultaneously harmonic with other peoples work in an often quickly changing landscape.