A minority portion of the premine is being staked to give the dev team a continual source of income that helps pay for both current and future expenses. We would not be able to professionally build and deliver Sigil Go, hire a developer to overhaul the wallet, hire a community manager, make great commercials, and do wonderful press releases without staking. Many incredibly successful projects, like Zcash and Dash, have found that a continual source of income is the secret to reaching a billion+ market cap. We use our staking rewards to further Sigil so that it also stands a chance of joining those ranks.