Realized Gain why subtract boot Receive, shouldn't you choose the smaller one and defer the tax

The Big Picture - Example 4 Stock Transferred (3 of 3) Return to the facts of The Big Picture on p. 4-1 However, because the transaction qualifies under $ 351, only $100,000 of gain is recognized The $100,000 of Transformation debt is treated as boot boot received The remaining realized gain of $1,500,000 is deferred # iMTI029, FFLE O BLE The Big Picture - Example 4 Stock Transferred (3 of 3) Return to the facts of The Big Picture on p. 4-1 However, because the transaction qualifies under $ 351, only $100,000 of gain is recognized The $100,000 of Transformation debt is treated as boot boot received The remaining realized gain of $1,500,000 is deferred # iMTI029, FFLE O BLE