Airport Management: Aviation Activity Forecasts

To assess the ability of Airport facilities to accommodate future demand and to identify the extent of new or expanded facilities required, aviation activity forecasts were developed for airline passengers, scheduled and other aircraft operations, and cargo tonnage. Based on the four graphs below from ATL airport, why is it important to make an assumption or predict future forecasts for the 20-year planning period? And why airports such as ATL airport developed based on historical and forecast relationships among enplaned passengers, load factors, and average seating capacities of aircraft types serving the Airport is significant to the operations?