Why do you believe this to be true? Many medieval manuscript illustrations of musicians feature someone playing drums.

As for modern re-creation of music, in very general terms musical notation that comes down from the medieval period is just the main melody - if it exists at all. For example, only ~10% of medieval troubadour lyrics come down with any musical notation...and only melody. Yet so many contemporaneous illustrations of musicians have a variety of instruments, including pipes, bagpipes, viola, fiddles, lutes, drums, other percussion instruments, etc.