Because of big volatility sometimes it is more profitable to trade EDC than to lease EDC for a long time. EDC has a big trading volumes and a good liquidity. It has listing on many exchanges.
Not all people can trade on exchanges and make profit on trading. Leasing program is good for those who do not want to trade or can not trade on the exchanges.
A lot of people participate in leasing program and most of them prefer to lease tokens for 12 month.