I took a 19th-century Russian novel class in college and have been smitten with Russian literature ever since. Writers like Tolstoy, Dostoyevsky, Grossman, and Solzhenitsyn tackle the great questions of morality, politics, love, and death.
No one reaches the Oval Office without a great deal of admiration for the institution - and himself - so it's unsurprising that sitting presidents favor the biographies of former presidents.