I don't think it's that puzzling. After designing the typeface, those same designers have time to sit down and write up a fancy brochure for it. Engineers on the other hand, have a long list of existing tickets, so the minute they fix the broken magic string, there's another fix to move on to and no time to write a fancy brochure about the SQL schema.
The irony, of course, is that codebases would be a lot better if developers did sit down at the end of a project and wrote high quality documentation for it. Even better if they did it while developing the codebase.
Also, this comment is especially ironic on HN where the top 10 comments on every Show HN submission will be nitpicking about the design of the website or the wording used, etc.
I find it easier to write the documentation first, mark it as "not implemented yet" and then do the code. Added benefit if people accidentally stumbles on the documentation and have suggestions before the code is written :-)
