I think author's are just scared of writing unhinged, disgusting GLs because everyone considers GL as a genre that exclusively needs pure love stories, idk tho.
Anyway, here are some (sort of) cannibalistic GLs:
https://www.mangago.me/read-manga/a_lady_s_table/
https://www.mangago.me/read-manga/futsuu_to_bakemono/
https://www.mangago.me/read-manga/harapeko_kopeko_wa_niku_to_sumu/
https://www.mangago.me/read-manga/chimidoro_ice_cream/
https://www.mangago.me/read-manga/a_monster_wants_to_eat_me/
Just watch Yellowjackets
Cannibal bloodthirsty sapphics, pick ur fav horrible person lol
How would you guys genuinely feel about a gl like killing stalking except remove all the sa scenes but it's where a Cannabol kidnaps a girl planning on eating her not exactly like killing stalking but it was the only thing I could compare it to