Unlevered net income

Why exactly does the derivation unlevered net income from net income add NET interest expense (interest expense MINUS interest income)—as opposed to simply adding only interest expense WITHOUT caring to artificially subtract interest income?? It sounds a bit counterintuitive to me if the ONLY goal of deriving an "unlevered net income" is to be ”capital structure–agnostic"—as whatever debt a company chooses to invest in buying ought not to concern the company's own internal capital structure which the interest expense already accounts for.
Interest income is merely an inflow from investing activities—why then does it get involved in the equation, if only interest expense reflects whether or not the company is indebted?