While running an IPFS node does supply some utility to the DHT, the primary utility you can provide to the network is providing files.
You only provide files that you have previously accessed via IPFS or added yourself. So even without any external motivations to sponsor other people's content (which are in the works), you have the motivation of sponsorship of content that you wish to increase the robustness and accessibility of. Increasing access to public utility can be itself an incentive.
