I think it's easy to underestimate how valuable something like a Facebook account actually is.
If I meant someone real harm and had access to their Facebook account, I could cause them a lot of trouble. I could send messages to their friends asking for unreasonable favours, starting arguments or causing other offence, I could embarrass them in front of their family. I could stalk them in real life. Look what happened when 4chan got hold of the passwords to a bunch of Christian student Facebook accounts: