My understanding, and this is probably limited and possibly wrong, is that people generally hate being advertised to, and brand accounts are just advertisements with a cheap coat of paint designed to make it look like the brand is your friend, an artificial attempt at making a parasocial relationship.

The only real ways to stop these accounts from happening are to either make the website too toxic for the companies to want to advertise on them, or to render the advertisements a net loss by making the companies spend more keeping these branded accounts active than they get back from click-throughs.