Not sure the truth behind this since as we know everything we read on the internet is true, but I've seen reports and comments state that MGM does not want Epix to be included in packages, they want it a la carte only and as carriage agreements that were made under the Viacom ownership expire, Epix will become a la carte only.
That does seem to follow the pattern. When Comcast picked up Epix last year it was added on an a la carte basis only. About a year ago Charter stopped including Epix in the TV Gold package and made it a la carte only for new subscribers. Grandfathering for existing subscribers ended in February of this year.
The $6 price point is something that has been maintained. While the a la carte prices of HBO or Showtime vary from one MSO to the next by a dollar to two, $6 seems to be the rate for Epix. That's what Comcast is charging for it, Charter was charging $15 for it, but it was dropped to $6, Orby added it recently for $6, and now we have DirecTV charging $6.