Companies do it because it works. You're blaming bad behavior on the people that are being manipulated because, according to you, they have psychological problems. As if the people being manipulated being disabled somehow excuses the company taking advantage of them.
Exactly. Taking advantage of vulnerable people is not a legitimate defense, the fact that they are easily exploitable makes the behavior even less moral.
Parental manipulation works because it's completely reasonable given the relationship for it to be effective. It's a betrayal of trust.
If a company tries that tactic and it "works" too well, that's an opportunity to evaluate your psyche, not get mad at them.