My best guess? Ricardo realized a few things:
Up to this point Ricardo had done a passable job of using Shan as his own personal meat shield - too good of a job maybe, though, because Shan was getting 100% of the credit for any game moves. In a Ricardo/Shan F2, there was NO way Ricardo had a chance in hell of beating Shan.
Pretty much the only reason people were currently targeting Ricardo was because of his association with Shan. No Shan? No target!
Should Ricardo make it to F2, burning Shan (his primary ally) to go further would be a helluva major note on his Finale résum