51. Read the following passage, then answer the question below.

Financing infrastructure projects in Indonesia's outer regions presents a distinct set of challenges compared to projects in major urban centers. Lower population density and limited local revenue make it difficult for regional governments to attract private investment without central government support. To address this, the national government has introduced blended financing schemes that combine state budget allocations, regional transfers, and concessional loans from development partners. While these schemes have enabled the construction of roads and ports in previously underserved areas, some economists caution that heavy reliance on external loans could increase regional debt burdens if project revenues fall short of projections.

What challenge does the passage primarily discuss?