Why "ruled supreme" instead of "ruled supremely"?

In this sentence:

With George, his perfect manservant, and Miss Lemon, his perfect secretary, order and method ruled supreme in his life.

Why is ruled followed by supreme instead of by supremely?

Use of adjectives rather than adverbs in such constructions is common. The adjective modifies not so much the verb as the verb’s subject. Such adjectival predication is by no means confined to such more or less copulative verbs as be and seem, but works with more active verbs as well. Thus New Hampshire’s license-plate motto, which is controversial only for its belligerence, not its grammar:

Live free or die.

Or for a more august exemplar, try the opening of Lamentations of Jeremiah, in the 1611 King James Version:

How doth the city sit solitary, that was full of people!

Participles can work in this way too. Many a candidate for office has been said to “run unopposed.”

To rule supreme is something of a "fixed collocation", meaning rule unchallenged...

supreme - highest in rank or authority; paramount; sovereign; chief. _^(Source)

To rule supremely (a relatively uncommon usage) would mean rule exceptionally well...

supreme - very ​great, or the ​best. _^(Source)