Imports are considered a leakage factor primarily because the money paid to producers of imports leaves the country. When consumers buy imported goods, the money spent goes to foreign producers rather than being circulated within the domestic economy. This outflow of money can reduce domestic income and spending, as it does not contribute to the local economy or support domestic industries.
While the other statements touch on related concerns—such as the impact on domestic industries and potential taxation—the core reason imports represent a leakage is the direct outflow of funds from the domestic economy.