I do believe that some sites do cross post from, say, a forum, to Facebook and I suspect with the intention of directing traffic back to the forum - which may, like the MSC, have some paid for options, so just getting extra traffic may well increase the income, and why not...
Personally, as someone who has worked in IT for a good number of years, I do have problems with FB, their business model and a few other things; after all with all the valuable data they are getting from their members I don't see why they shouldn't pay you to post on FB !
On balance I do find that more-or-less single subject sites like the MSC are the most useful (have more useful posts, less spam etc.) and I do tend to use them a lot so I certainly hope that they do/will survive...