All unsold tokens will be airdropped to token holders, in order to create an ecosystem around the ECO token we need the full amount of the total supply to enter the market eventually. Other considerations are that, if the tokens are burnt, then the ratio or percentage that the developers hold would increase to more than 15%, so in order to develop a balanced ECO system, we want to airdrop the unsold tokens in the correct ratio's.
Token holders often complain that after ICO's, developers have much more than the original ICO percentage because of unreached hard caps and burnt tokens.