I see three main reasons why developers should write:

1. Sharing knowledge: communicate their ideas and thoughts to a larger audience and help others learn more
2. Building a personal brand
3. Learning: writing can be a way to structure their thoughts and consolidate their knowledge

However, there are many other ways devs could reach the same objectives.

1. Use videos or teach live lessons
2. Be a speaker, panelist, building in public, contributing to projects etc.
3. Using diagrams, building prototypes, or just reading

So, why do you write or don't write?