I think the pressures of collecting have something to do with it. Many of the one's today appear to be from deeper waters. They is some discussion that with the skimmers etc. our tanks are too clean to support them??? Who knows for sure?? My tank is VERY filtered with moderate flow with lots of LR and Medium light levels. It is a sand bed creature that need to be by its self to prevent abrasion to its tentacles against the LR etc. I feed mine (that MONSTER) twice a week with all kings of foods. Also the tank gets a big daily dose of DT's in the tank once a day.(not that he eats it)
He will sometimes retract more after a good feeding and become darker in color for a day or two at times. I think that is normal.
All the good old reference materials point to this coral being very hardy years ago.
The examples and the way they are kept at the LFS's have a bearing too. Most I have seem in LFS"s are already half dead!!!!!
This is a paste from a post I did last year. I lost mine afer about 8 or 9 months when moving to a new home
Here are a couple old shots of him/ Good Luck..........