Final answer:
The key factor that limits a large community's ability to influence policy compared to a special interest group is the lack of financial resources.
Step-by-step explanation:
The main factor preventing a large community from influencing policy in the same way as a special interest group is lack of financial resources. Special interest groups often have significant funds at their disposal, which they can use to support political candidates, hire professional lobbyists, and engage in other activities that help to raise their concerns and proposals to policymakers. This financial capability gives them a distinct advantage over larger communities, which may have substantial membership but not the same level of economic power to influence policy decisions.