Regardless of who's side you're on in this you have to accept that the value of what's contested (who came up with / owns / started Facebook) is worth much, much more than ~$65 million (the original settlement amount). Call it greed or call it white-collar entitlement, but these guys seem serious about seeing it all the way through. Who wouldn't? No sane lawyer is going to advise them to settle for a fraction of what they might actually have a legal right to. Too much money is on the table.
The crux of the argument (for me personally) is whether or not these guys hired Zuckerberg to build the original version of what became Facebook. I've not read up enough to be convinced either way, but again, lawyers will weigh the options and advise accordingly. At the end of it there will at least be some more case law around who-owns-what under similar circumstances.