Why use git submodule, when the repo already use CMakes Fetchcontent?

From CMakeLists.txt

# Prefer the in-tree submodule when present; only fall back to fetch.

	▲	macgyverismo 3 days ago \| parent [-]
		That explains it. I guess my actual question was, why would you prefer submodules over fetchcontent :)

tfeayush 3 days ago | parent | prev [-]

I don't know like to see it all connected on the Github web interface.