Goodwill? I don't think it's really a "desperate last-chance measure", so much as a tool. FB and Google both offer a lot of other services beyond just chat. FB offers photo sharing, the newsfeed, potential for correct address books (at least with people that share that info with their friends), event organizing, games. I'm not that into it, but I know a lot of people that are. Then Google offers Google Mail, Docs, Hangouts, Calendar, Drive. I think they have their own image sharing system (I don't take many photos, so those features are nearly useless to me). Their chat protocols are more of a side-effect of having something already associated with your identity. Opening them up to federation likely won't cost them many users (and those users it does cost them will likely be as inactive on all their other services as I am), but has the potential to gain goodwill and endorsement from other circles (particularly those people that others -- family, friends -- go to for tech advice).