Machiavellian, draconian and quixotic

A bit of a puzzler today.

The adjective 'Machiavellian' (meaning "cunning, scheming and unscrupulous, especially in politics or business", OED) is derived from the name of the Italian statesman and writer Machiavelli (1469-1527) - the chap pictured on the left.

Similarly the adjective 'draconian' (meaning "(of laws) excessively harsh and severe", OED) is also derived from the name of an individual - in this instance the ancient Athenian legislator Draco.

So why is it that Machiavellian takes an upper-case 'M' but draconian doesn't take an upper-case 'D'?

I tried to think of some other examples to see which camp they fell in but didn't get much past 'quixotic' - which is derived from the name of a fictional character anyway. Obviously I am discounting adjectives such as Jacobean because they relate to the individual's life and times rather than their personal qualities. Anyone help?