It seems I hadn’t thought about the interaction between git LFS and Netlify.
I found the answer in this thread.
I’d maybe just suggest to add this environment variable information (GIT_LFS_ENABLED and GIT_LFS_FETCH_INCLUDE) to the Large Media Setup docs, because these are interconnected, yet the variable information is only specified in the general environment variable section.
Seems like these two variables should just be added to the large media section to prevent issues like mine from happening, especially for people like me, who hadn’t worked with both Netlify and git LFS before.