This isn't my area, but here is a link to a recent thread concerning views of feudalism and whether it actually existed. Here is another thread on the topic.

Both of these are available on the FAQs page (not that there's lots more that can't be said on the topic!)

I'll summarise the common view on feudalism and it's 'origin'.

Feudalism was 'created' by sixteenth-century lawyers trained in Italy studying from the Libri Feudorum ('the Book of Fiefs). The lawyers and antiquarians of the sixteenth- through eighteenth-centuries envisaged medieval landholding as centred on the fief. This was concept was soaked up by nineteenth-century historians and, in the twentieth-century, this exploded into a holistic analytical model which drew on northern French society and culture to create an 'ideal type' which could then not only be compared to other contemporary societies but to periods and places where fiefs and vassals had never existed as terms. This is a somewhat barebones sketch but I'm rather tired about discussing the subject. Essentially you're right, no king did say those types of statements. It was the development of a more professionalised legal class in the twelfth- and thirteenth-centuries which began the process of codifying the tenurial patterns and superior/inferior relations which would lead their sixteenth-century descendants to begin conceiving of fiefs, and later for historians to conceive of feudalism.

Those are the origins of feudalism. Your other question on why democracy/republicanism/etc. didn't survive is something completely different and unrelated to that historiographical one. It also probably won't be answered as its hidden under the aegis of feudalism.