We had planned a token sale to raise funds through the sale of OMG tokens. However, a token presale offered to the earliest OmiseGO community (with no preferential pricing for anybody) received such high interest that the goal amount of $25 million was raised just through that - without having to run an on-chain sale (even though far more would have been raised if we had chosen to do so.)
We wanted as many people as possible to be able to participate, without taking more money than we thought we needed. We thought we needed $25 million to create and launch the network, and we felt that taking more than that would be irresponsible. We wanted people to buy in because they believed in the long-term vision, so we intentionally did no marketing or promotion, including not offering discounts to incentivize people to buy more tokens.