Most cryptocurrencies like Bitcoin, Litecoin, Dash, Dogecoin etc are very volatile. Merchants do not like volatility because it forces them to immediately offramp their cryptocurrency for fiat currencies such as dollars, euros, yuan and so on. Smartcoins however are market-pegged assets (aka: MPA's). So, a bitUSD follows the value of 1 US Dollar, 1 bitCNY follows the value of 1 Chinese Yuan, 1 bitSILVER follows the value of one troy ounce of silver and so on. This makes Smartcoins much more preferable to merchants to acquire, and hold, instead of having to worry about price fluctuations. Smartcoins are also much more scalable (over 100,000 transactions per second have been proven so far) and faster (transactions take 3 seconds or less). There are probably more reasons than that, but those few reasons alone are why we switched our products onto the Bitshares platform because it just has so many more options for app builders, businesses, traders and investors. There is a nice page that explains more about Smartcoins here: http://bitshares.org
Those are just my opinions of course, but I hope that helped a bit :)