I am not gonna speak for this compound in particular but there are a myriad of reasons why some very promising drugs never make it to market. First of all, it costs millions of dollars to get a drug approved and so not every promising drug is applied to the FDA for approval. Many times there are intellectual property issues involved, or the market for the compound is just not fertile enough to invest in. In the case of steroids I can probably name you over a hundred excellent anabolic steroids (out of Vida's book) that never made it to market. Many of these might have been as good or better than what is currently on the market but it just was not worth it to the drug companies to go forth with at the time. They have to pick and choose what drug candidates to invest the dollars in and that leaves alot of drugs in permanent limbo. Usually these are protected by patents so no one can steal them and market them (patents do run out in 18 years though).
As for this nandrolone ether I really don't know if it is really that good or not. It probably is no better than currently available compounds so I doubt that the company that originally synthesized it 40 years ago ( I believe it was an Italian company called Vister) found it worthwhile to bring to market.