Because people want to evaluate the company's trustworthiness (or more precisely, the trustworthiness of its leaders and culture).

In this case, if they refrained from selling data due to ethical principles, you can put more trust in them, at least for a little while. If they only refrained because they didn't think they could get away with it now, they'll probably sell your data the first chance they get, so you can't trust them as much.

However, Facebook's already clearly demonstrated its' true colors many, many times, so it's kinda a waste of effort to reevaluate it.