Here is the Official statement that Hellfest posted concerning the band cancellations:

“Recently, you may have noticed that the « Running Order » of the Hellfest 2014 edition tends to suffer of cancellations and/or schedule changes…
Though we definitely take a lot of risks by programing more than 160 bands each year, we would like to make things clear in order you, the festival-goers, not to reconsider our main goal: satisfy YOU!

Questions gush out on social networks: why all these last minute schedule changes? Why all these cancellations in such a short period of time?
Be assured that we are the first to be awfully sorry to be forced to announce these “bad news”, especially since we are far from being the ones to blame…
Indeed, all over the year, the Hellfest team works on the development of the site and the setting up of a coherent program, based on commitments founded and confirmed by the bands, via their agents and managers. All of that is an upstream work, more than 6 months (sometimes even more) before the opening of the doors.
Personal reasons/pretexts, sudden unavailability, poor organization of tour routes, abusive financial re­-negotiations and ego/fame problems… any excuse bands can to avoid their commitments and to put sick pressure on the festival organization in order us to yield to their desiderata.

The more the years go by, the more some artists grant themselves liberties and the “luxury” to change, by instance, their timetable at the last moment, without, of course, caring about the disruptions linked to this, and even less about the complainers it creates… which fall, obviously, on festival organization’s back.
So today, thanks to all the (too) many negative comments we have to face, we have decided to say STOP, and that it’s our time to yell out. To yell out about all those artists who too often forget that the first reason of their participation to an event like the Hellfest is, before everything, to please the audience and to share emotions with YOU, the fans! And not to demand any preferential treatment that will, in the end, be prejudicial to all who make sacrifices to come applaud them!

Since its creation, the Hellfest has always been a festival organized by fans for fans… And even if we sometimes have to give in under some bands lobby, the Hellfest shall always be a festival organized by fans for fans…

We would like to apologize once again about the troubles caused by these last minute changes. But be aware that this kind of situations saddens us as well…
Having said this, we have to once again announce “bad news”, because the bands ICED EARTH, MGLA, and ALUK TODOLO have just let us known about their cancellations… The bands BORGNE and BLACKLODGE shall stand in respectively for MGA and ALUK TODOLO.

Hoping that all of that shall not tarnish the party we planned for the 20th, 21st, and 22nd of June in Clisson… Two weeks to go…”