Gonioporas fare badly mainly for 2 reasons...
1. If you read up on their habitat, they are usually found in murky, sediment laden waters rich in nutrients. Most aquariums do not provide these conditions, even underskimmed tanks won't be murky...Unless you make it a point to design a murky tank. All corals need a source of protein. They can either obtain it from dissolved nitrogeneous compounds or from live prey. I've never seen gonioporas actually capture and ingest prey like artemia nauplii but then again they could possibly be capturing prey invisible to the ###### eye (Bacteria species, etc).
2. Most gonioporas succumb to bacterial/other pathogenic diseases shortly after being collected. Generally it has got to do with their handling when they are being collected. As gonioporas are generally quite abundant in the wild, the collectors who sell them to middlemen earn very little. They make up for this by collecting more and crowding them in holding vessels probably leading to physical damage of individuals. If you think about the common flowerpot coral, it does take quite awhile for them to shrink down fully into their skeletons. Lifting them out of water before this happens can very easily lead to tissue damage and subsequent infection.