I said in the wild because they don’t have a trainer to carry that sort of bond with. So do all members of the ralts line just naturally have that mentality, even if they don’t have a trainer? If so, why don’t other human-like Pokémon have that (specifically other psychic human-like Pokémon such as Alakazam, Jynx, Mr. Mime, Medicham, and ESPECIALLY Gothitelle!)? What makes the ralts line so special here?

You’ve actually hit the nail rather on the head right there: they naturally have that mentality. Keep in mind that ralts are naturally highly psychic and become attuned to partners based on empathic probes first and foremost, not to mention the fact that most wild pokémon seem to be aware of humanity (seeing as wild pokémon can choose to venture out and find trainers or withdraw further into the wilderness to avoid us). Whereas alakazam, jynx, and so forth are attracted to like minds, for the sensitive members of the ralts line, they’re repelled by anything they consider a potential battling partners and caretakers—i.e., humans. Thus, they’re also repelled by anything that reminds them of humans, even if they themselves have never spent time with our kind.