I think it is because BG’s last longer and make more money than GG’s
Compare the number of active 2nd gen BG to that of girl groups and you would see the difference.
Even for other companies
YG:
BG: Ikon , Winner, BG(hiatus)
GG: Black pink
Pledis
BG: Seventeen, Nuest
GG: RIP Pristine and After...