I think the competition from the .22 conversion kits are what really killed it. Even at today's prices, you can spend under $200 for the conversion kit, and have $450 left over for .22 ammunition. I can buy a LOT of .22 ammunition for $450!
Then add in the air tanks or a pump and such required for a PCP and for the average AR-15 shooter, it really doesn't make sense. And to top that off, I believe it came out before the PCP Air Rifle revolution really took off. Fantastic design, but over priced for a very limited market segment.
To add to the complexity, if I want to shoot my pellet gun in the back yard, it's pretty much legal. If I want to shoot the MAR-177 in the back yard, it's still considered a "Fire Arm" because it sits on a registered gun (lower). I'd love to have one, but considering for the price I could buy a Marauder or three Maximus rifles or two Gauntlets, you can see the limited appeal.