What the fuck is a steel type weak to?
Fire, Fighting and Ground. Fire can melt steel, earthquakes can topple steel structures, and martial artists are usually depicted in fiction as capable of breaking steel (incidentally, martial artists also commonly break bricks/concrete slabs and ice blocks, which is why Fighting is also strong against Rock and Ice).
They're weak to Ground and Psychic. Ground can absorb toxins. Psychic is kind of a stretch, but kinda seems like poison acts as doping for the mind.
Fairy strong against Dragon, Dark and Fighting but weak to Poison and Steel
Yup! Fighting types are technically Hero types in Japanese, who usually fight head-on, making them a poor matchup against mischievous fairies. Fairies are also usually depicted as beings of light, so that's why they're strong against the dark.
Meanwhile Fairy beats Dragon purely because Game Freak decided dragons needed to be nerfed. I personally think of the Chesterton quote: "Fairy tales do not tell children dragons exist. They exist to tell children dragons can be killed."
Poison beats Fairy by the same logic they beat Grass-- pollution destroys nature. Steel beats Fairy because iron is a common weakness of fairies in folklore.
Ghost is weak/supereffective to itself, and also weak to Dark
Ghosts can touch other ghosts, and easily corrupted by evil.
Dark represents evil, while bug represents heroes (in Japan, bugs are well liked and often form the basis of tokusatsu heroes). And heroes always prevail against villains.
Bug being resistant to fighting while also super effective against both Dark and Psychic
And so by that logic, Bug is resistant to Fighting because some of the strongest enemies a hero can face are other heroes.
Bugs thrive in darkness, and their minds are too alien for espers to affect.
That's about it, thank you for coming to my TED talk.