Game theory,

and only a theory:

B. Writer of presidential bios, like all writers, needs publicity and royalties.

I. Writer does an appraisal of trendy subjects.

N. Writer finds suitable trendy subject: gay issues.

G. Writer looks at surveys of popular presidents.

O. Writer finds a popular president who’s dead, and whose descendants aren’t likely to sue: Lincoln.

Writer does math: Popular, dead president + trendy subject = BINGO

I’m such a cynic.