The oldest known neuf preux are here in Cologne, possibly between 1350-70, possibly earlier. In the city council.
Cologne was important for emperor Charles IV, that's the reason. As a Luxemburger Charles IV (though mainly in Prague) had close relation to the Northern France region, which itself had close nearness to the Brabant region.
That's the region, where the Neuf preux spread. Cologne - Netherlands, that are about 80 km, not more.
From the 7 Kurfürsten with the right to chose the Roman king, three were the arch bishops of Cologne, Mainz and Trier. These 3 cities are close to each other (look at a map), actually they are only a small region of that, what is now and earlier understood as "Germany". Cologne and Trier had been the most important Roman cities. Chlodwig had fought a major battle in Zülpich, that is maybe 25 km distance to Cologne. Charlemain had his center in Aachen, which is about 75 km from Cologne, another in Ingelheim , which is near to Mainz. This all had been a powerful region, thanks to the river Rhein, where all the trade took place, and very good agriculture possibilities around Cologne, where the region more or less is flat. The center of Luxembourg is very near to Trier.
A powerful center in the past: The Romans reigned in their German region often from Cologne. From here the German empire expanded towards the East. In the development the emperor took his seat in the East at various locations, mainly in Bohemia and Austria, much later in Berlin, but the old center had been here. After WWII the center dropped for some time back near to Cologne, to Bonn (25 km distance from Cologne).
So Emperor Charles VI had from the older connections a clear interest in the region, when he started to be an emperor.
Well, his grand-grandfather had died in the battle of Worringen (1288), that's here, near to Cologne, when the current Cologne arch bishop had trouble with the Cologne citizens. The grand-grandfather had an error and fought on the wrong side (against the citizens, with the arch bishop), so he was dead after the battle and the citizens reached some independence (and the arch bishop was disallowed to enter the city mostly).
His grandfather became surprisingly German king (1308) and emperor (1312) and died (1313) in Italy. It seems likely, that the work of Jacques de Longuyon of Lorraine, Les Voeux du paon (The Vows of the Peacock), written for Thibaut de Bar, bishop of Liège in 1312, actually were done for the crowning ceremony in Rome. Thibaut of Bar died there, too, in 1312 already.
"Les Voeux du paon" is the origin of the nine worthies. Actually the poet was unlucky, cause his sponsor died, but later (in the 1330's till 1340's) Baldouin from Luxembourg, arch bishop of Trier, engaged strongly for the Luxembourg dynasty in Bohemia and caused to a good part, that Charles IV became emperor against a still existing, but often disputed emperor, Ludwig IV. of Bavaria. It seems, that the new popularity of the "Les Voeux du paon" played its certain role around this time.
One has to remember, that one of the 9 figures of the neuf preux, Godfrey of Bouillon, was from the perspective of a bishop of Liege a "local hero", similar Charlemain had been chosen from the "neighborhood" (the distance Aachen - Liege is short)
The idea of the neuf preux was political propaganda for a new emperor (partly Henry VII, partly Charles IV.), and this new man was backed up with the proud background of famous other examples.