Also I don’t get why the code has been spread out in a bunch of different folders and files rather than following the regular conventions for WordPress themes.
I recommend reading the README, which explains why the theme is organized as it is.
However, I’m a bit annoyed at all the self – promotion. Seems a little bit contrary to the spirit of open source.
…
And then every single file has a promotional section.
This is not promotion or self-promotion. It is following the guidelines of the FSF:
https://www.gnu.org/prep/maintain/html_node/Copyright-Notices.html
You should maintain a proper copyright notice and a license notice in each nontrivial file in the package. (Any file more than ten lines long is nontrivial for this purpose.) This includes header files and interface definitions for building or running the program, documentation files, and any supporting files.