Now GF are part of a Big Hit subsidiary, MBC & Big Hit don't get along. Thus MBC have kind of been blocking all artists associated with Big Hit from appearing on their network, including chart shows.
Yeah, i think i read abt tat when a year end show in 2019 dint hv gfriend on as possibly retaliation for bts appearing in US new year's eve show ibstead of theirs, but i'd forgot which show it was, gayo daejeon, or gayo daechukje or i now know mbc's gayo daejejeon. It seems i remember reading each big 3, except jype-SM, YG n now BH/SouMu hv beef with some weekly chart show or other, except maybe SM's beef may be over.
I saw tat u posted all 3(RV:I&S, BP n GF)'s stages on Inki today but disappoint when noticed gfriend dint see then at the encore n their stage seemed like it was prerecorded so no RVBPGF on stage at same time today.

Here's:
a look at behind of gfriend song "Apple" abt the writing of lyrics n recording the singing.