If you look in the medical industry for example ethical decisions are always managed by a different group than Product/Legal because it's a completely different set of skills and competencies.
Even more so at places like Twitter which are heavily dependent on ML models to make real-time decisions. And so you need a dedicated team that is proactive rather then reactive like a Legal team would be.
Putting the "what will our users think" question in an ethical framing is not obviously (to me) going to benefit users. (Especially when modern fashionable ethics centers around utilitarian normative ethics, but that's besides the point.)
Some companies, such as for instance Procter & Gamble or Apple care about their brand equity a lot, since they rely on it to charge above market premiums. Twitter needs to care about that too, since if they get caught doing something unsavoury they will turn toxic to their advertisers, or at least those who care about their brands. I am not a marketing exec but if Twitter now drops the pretense of caring about ethics you will see major advertisers pull out, and make a point of communicating why they do it. Thats the ROI on having functioning ethics teams.