This only shows the naivete of the author. There are plenty of C programmers that aren't malloc abusers and like to avoid any potential syscall usage. Instrusive linked lists is a beginner C topic.
Your comment makes it sound like everyone should do this. Are there not reasons to have a non intrusive list as well? For example if the structure is used elsewhere and you don't want to tie it to that list implementation. Or if you want to point to the same structure many times in a list?