Given corporate taxes, why does adding debt to the capital structure increase firm value?

$1)$ Extra cash flow goes to the firm's investors rather than the tax authorities.

$2)$ Earnings before interest and taxes are fully taxed at the corporate rate.

$3)$ Personal tax rates are the same as marginal corporate tax rates.Given corporate taxes, why does adding debt to the capital structure increase firm value?

$1)$ Extra cash flow goes to the firm's investors rather than the tax authorities.

$2)$ Earnings before interest and taxes are fully taxed at the corporate rate.

$3)$ Personal tax rates are the same as marginal corporate tax rates.