Their "mass of BTC profit" isn't from their pool.  Their pool costs them money, it makes them nothing.  It has, from day 1, made absolutely no economic sense for their pool to exist at all.  Their private farm is as large or larger than any other pool as is, so the argument of letting others join them to reduce their variance is moot.  They're too large for variance to make an impact on their monthly revenues.  They're paying to run servers for people for nothing, unless they're skimming from the top.