Copycats and government intervention in other words.
OK, let's say you forked the bitcoin chain right now. Would you expect robm-coin to be more succesful than the main chain? If so, why? If not, why would other copycats be better off?
If you don't agree on a currency you can't trade, it's as easy as that. Which means that it pays off to use a chain/cryptocurrency that other people use as well.
They could be more successful if they were easier to use, easier to obtain. Perhaps the distribution through mining was too steep with Bitcoin. Perhaps someone creates a slick new client for theirs that is easier for casual users to have. Perhaps someone markets it better. I guess you guys are all on Friendster since why would anyone ever displace them since they were first to market.