Oh I'm aware. My guess is because Poison types were so ludicrously plentiful at the time they had to "nerf" them by not giving good (if any) STAB options. Not that it mattered either way since the broken Psychics annihilated them.Not that there was much to choose from. Sludge was the most powerful at 65, and was exclusive to Muk and Weezing. Arbok, Vileplume, Victreebel, and Tentacruel got Acid as their best poison move at 40 power. Beedrill, Nidoqueen, and Nidoking got Poison Sting at 15 power. Venusaur, Golbat, Venomoth, and Gengar got nothing but status moves(Toxic for all four and Poison Powder for Venusaur and Venomoth). The only other Poison damage move in Gen I was Smog, which was exlusive to the Koffing line.
Gen II was somewhat better when Sludge Bomb was introduced and made a TM but Venusaur, Nidoqueen, Nidoking, Gengar, and Crobat were unable to learn it until Gen III.