This is the first meaning of the word derivative used as an adjective(Oxford):
1 (Typically of an artist or work of art) imitative of the work of another person, and usually disapproved of for that reason[...]
This is seemingly the only use case where you have this negative connotation. One can trace the etymology of the word:
early 15c. (adj.); mid-15c. (n.), from Middle French dérivatif (15c.), from Late Latin derivat-, past participle stem of Latin derivare (see derive). Mathematical sense is from 1670s.
This is very much about things branching out/away, such as a river etc. Yet as late as the late 19th there doesn't seem to be any reference to this idea of disapproval nor to any negative undertone whatsoever(Century Dictionary, 1895):
Derived; taken or having proceeded from another or something preceeding; secondary: as, a derivative word; a derivative conveyance.[...]
Q. When does that idea appear in the English language? And in what context? A negative association with derivatists?